1. Introduction
Solvability of nth degree polynomial equations has been challenging to mathematicians over centuries, especially when looking for algebraic terms to express the roots. This challenge is due to the complexity of calculations that can exceed the previsions of human mind especially when degrees of polynomials are making them surpassing the quartic form.
The complexity of calculations during the attempts of solving polynomial equations of high degrees is mostly due to using radicalities while adopting specific approaches. In addition, reaching a point of having high complexity of outcomes where the form of equation is far from foreseeing a reduction; will lead to conduct a radical change on used approach or even replace it by adopting a different one.
Adopting a specific approach to solve a specific degree of polynomial equations lead to have limitation in resulted forms of equations where reductions are harder to be conducted by comparison to the starting point. In addition, conducted calculations may augment in high rate when searching for the solution by trying different approaches that may lead to restart calculations from scratch. Furthermore, the complexity of resulted forms of equations may lead toward adopting a limited solution to be used on a specific form of polynomial equations that have specific conditions stated by the values of included coefficients.
As a results, finding unified solution formulas for polynomial equations in general forms and in complete forms is more challenging when relying on a research methodology where calculations and logic may to be restarted from scratch when the approach is radically modified or even replaced.
Therefore, we rely on an engineering methodology where we build the appropriate approach step-by-step basing on patterns and characteristics that should be met. Then, we use this approach to architect the adequate roots and to structure their involved terms and sub-terms. Then, we forward logic and calculations toward engineering the formulas of all roots, in order to allow the calculation of all expected solutions nearly in parallel.
Relying on this engineering methodology to solve polynomial equations avoid us restarting the logic and calculations from scratch, and allow us to keep relying on the same approach and results of calculations while conducting only slight modifications, when necessary, toward reaching the final forms of unified formulas. In addition, this engineering methodology allows us to project the same approach and extend the same logic toward solving higher degrees of polynomial equations.
In this engineering methodology, the axe of focus is building and architecting according to a scalable logic starting from requirements engineering toward designing the starting point, the path, the destination and the structure of expected final results. As a result, conducted calculations and adopted reasoning follow a pr-designed path toward structuring the unified formulas of niched roots.
The advantage of this paper is presenting two new theorems solving sixth degree polynomial equations in general forms by using radical expressions where the possibility of calculating the values of all roots nearly in parallel. One among these two new theorems is solving sixth degree polynomial equations without the quantic terms, whereas the other theorem is solving sixth degree polynomial equations in complete forms that include the quantic terms.
This paper is also presenting the engineered requirements and techniques that lead to architect the results of proposed theorems. Furthermore, this paper is presenting another theorem solving quartic equations in general forms which is essentially used to structure all the six roots of sixth degree polynomial equations in complete forms.
Each proposed theorem in this paper is developed according to a scaled logic along with a detailed proof step-by-step, where we rely on the results of engineered requirements and techniques to forward the design and development of expressions, formulas and proofs.
This paper is a principal step in our work of solving nth degree polynomial equations basing on projecting the presented methods and results in this paper on other polynomial equations with degrees higher than five, which will be presented in other articles.
The mathematician Ferrari Lodovico is historically attributed the credit of discovering a principal solution for fourth degree polynomial equation by the year 1540. However, since his discovered root expression required having a solution for equations in cubic forms, which was not published yet by Cardano Gerolamo at that time, Ferrari Lodovico could not publish his discovery officially and immediately. Nevertheless, Ferrari’s mentor, Gerolamo Cardano, did publish the discovered quartic solution by Ferrari along with the cubic solution in the historical book of mathematics; Ars Magna
[1] | Cardano, G. Artis Magnae, Sive de Regulis Algebraicis Liber Unus, 1545. English transl.: The Great Art, or The Rules of Algebra. Translated and edited by Witmer, T. R. MIT Press, Cambridge, Mass, 1968. |
[1]
.
The discovered cubic root by the mathematician Cardano Gerolamo
[2] | Dumit, D. S. Foote, R. M. 2004. Abstract algebra. John Wiley, pp. 606-616. |
[2]
for third degree equations under the polynomial form
x3+px+q=0 
does help Ferrari’s solution to solve quartic equations by reducing their expressions from the fourth degree to the second degree, but it does not directly help to properly define the four roots of any quartic equation. Therefore, when having a fourth-degree polynomial equation in general form, it is necessary to conduct further calculations to determine its four roots while relying on the solution of Ferrari Lodovico.
The proposed method by Cardano Gerolamo was also relied-on as a foundation base to solve particular forms of

degree equations; such as by using specific radical expressions under the form

where the values of n can vary in the range

, …, etc.
[3] | Osler, T. J. 2001. Cardan polynomials and the reduction of radicals, Mathematics Magazine, vol. 47, no. 1, pp. 26-32. |
[3]
.
Over the history of mathematics, there have been many elaborated methods and published solutions to solve polynomial forms of quartic equations such as Euler’s solution
[4] | Euler, L. De formis radicum aequationum cuiusque ordinis coniectatio, 1738. English transl.: A conjecture on the forms of the roots of equations. Translated by Bell, J. Cornell University, NY, USA, 2008. |
[4]
, Galois’s method
[5] | S. Janson, Roots of polynomials of degrees 3 and 4, 2010. |
[5]
, Descartes’s method
[6] | René, D. The Geometry of Rene Descartes with a facsimile of the 1st edition, Courier Corporation, 2012. |
[6]
, Lagrange’s method
[7] | Lagrange, J. L. Réflexions sur la résolution algébrique des équations, in: ouvres de Lagrange, J. A. Serret ed & Gauthier-Villars, Vol. 3, pp. 205-421, 1869. |
[7]
and algebraic geometry
[8] | Faucette, W. M. 1996. A geometric interpretation of the solution of the general quartic polynomial, Amer. Math. Monthly, vol. 103, pp. 51-57. |
[8]
.
The cubic solution was almost-always considered as an essential milestone for further research to solve polynomial equations of fourth degree and above
[9] | Bewersdor, J. Algebra fur Einsteiger, Friedr. Vieweg Sohn Verlag. English transl.: Galois Theory for Beginners. A Historical Perspective, 2004. Translated by Kramer, D. American Mathematical Society (AMS), Providence, R. I., USA, 2006. |
[10] | Helfgott, H. Helfgott, M. A modern vision of the work of cardano and ferrari on quartics. Convergence (MAA). |
[9, 10]
, such as the case of trying to elaborate a proof demonstrating that quantic equations do not accept quadratic expressions as solutions, which is further discussed in the published research results in
[11] | Rosen, M. 1995. Niels hendrik abel and equations of the fiffth degree, American Mathematical Monthly, vol. 102, no. 6, pp. 495-505. |
[12] | Garling, D. J. H. Galois Theory. Cambridge Univ. Press, Mass., USA, 1986. |
[13] | Grillet, P. Abstract Algebra. 2nd ed. Springer, New York, USA, 2007. |
[14] | van der Waerden, B. L. Algebra, Springer-Verlag, Berlin, Vol. 1, 3rd ed. 1966. English transl.: Algebra. Translated by Schulenberg J. R. and Blum, F. Springer-Verlag, New York, 1991. |
[11-14]
.
A particular solution for third degree polynomial equation was first found in the year 1515 by Scipione del Ferro (1465–1526), which was presented as a solution for some specific cases determined by the values of involved coefficients in the considered polynomials. However, the official root-form considered as a practical solution for cubic equations; is the discovered root by the mathematician Cardano Gerolamo, which is generally recognized as the base of further historical research on solving quartic equations and other specific forms of polynomial equations.
There have been other recent publications presenting research results dedicated to solve quartic equations where the used methods are built on reducing polynomial expression
[15] | Shmakov, S. L. 2011. A universal method of solving quartic equations, International Journal of Pure and Applied Mathematics, vol. 71, no. 2, pp. 251-259. |
[17] | Tehrani, F. T. 2020. Solution to polynomial equations, a new approach, Applied Mathematics, vol. 11, no. 2, pp. 53-66. |
[15, 17]
, whereas other published results are relying on the use of computational algorithms and numerical analysis in order to find the roots of polynomial equations with degrees exceeding the quartic form
[17] | Tehrani, F. T. 2020. Solution to polynomial equations, a new approach, Applied Mathematics, vol. 11, no. 2, pp. 53-66. |
[18] | Nahon, Y. J. 2018. Method for solving polynomial equations, Journal of Applied & Computational Mathematics, vol. 7, no. 3, pp. 2-12. |
[17, 18]
.
In the published research article by Tschirnhaus
[19] | Tschirnhaus, E. A. method for removing all intermediate terms from a given equation, THIS BULLETIN, vol. 37, no. 1, pp 1-3. Original: Methodus auferendi omnes terminos intermedios ex data equatione, Acta Eruditorium vol. 2, pp. 204-207, 1683. |
[19]
, he proposed a particular innovative method to solve polynomial equation

of

degree by relying on its transformation into a reduced polynomial form

with fewer terms by scaling the proposed idea of Descartes; in which a polynomial of

degree is practically reducible by removing its term in the degree

. The projection of this published method on quantic forms of polynomial equations is presented with more details in
[20] | Adamchik, V. S. Jeffrey, D. J. 2003. Polynomial transformations of tschirnhaus, bring and jerrard, ACM SIGSAM Bulletin, vol. 37, no. 3, pp. 90-94. |
[20]
.
There are some other published articles treating resolvable forms of quantic polynomials by relying on the use of radical expressions
[21] | Lazard, D. Solving quintics in radicals. In: Olav Arnfinn Laudal, Ragni Piene, The Legacy of Niels Henrik Abel. 1869, pp. 207-225. Springer, Berlin, Heidelberg. |
[22] | Dummit, D. S. 1991. Solving solvable quintics, Mathematics of Computation, vol. 57, no. 1, pp. 387-401. |
[21, 22]
; in which we can find the description of specific criteria predetermining whether a quantic polynomial form may accept plausible roots with radical expressions or not. In addition, there are other published papers treating the resolvability of some equations with polynomial degrees higher than five while using factorization or by conditioning the forms of coefficients to be depending on each other
[23] | Samuel, BB. 2017. On Solvability of Higher Degree Polynomial Equations, Journal of Applied Science and Innovations, vol. 1, no. 2. |
[24] | Samuel, BB. The General Quintic Equation, its Solution by Factorization into Cubic and Quadratic Factors, Journal of Applied Science and Innovations, vol. 1, no. 2, 2017. |
[23, 24]
, which do not solve neither quantic equations nor sixth degree equations in general forms.
Some polynomial equations of sixth degree in simple forms, such as

, can be solved by factorization or by relying on variable change, but other sixth degree equations in complete forms could not be solved over history
[25] | Pesic, P. 2004. Abel’s Proof: An Essay on the Sources and Meaning of Mathematical Unsolvability, MIT Press. |
[26] | Wantzel, P. L. 1845. Démonstration de l'impossibilité de résoudre toutes les équations algébriques avec des radicaux, J. Math. Pures Appl., 1re série, vol. 4, pp. 57-65, |
[25, 26]
, until nowadays by using the presented solutions in this paper, which make the content of this article valuable.
The proposed concept in this article about architecting solutions according to a distributed structure of terms can extend itself to different problems in geometry, numbers theory and algebra in general; because this concept is introducing an engineering methodology based on identifying patterns and characteristics that allow forwarding calculations and expressions toward specific converging points where the results are built step-by-step and not only searched.
The used engineering methodology in this paper can also be projected on prime numbers by architecting the expressions of odd numbers according to a distributed architecture of terms, which may reveal (or prove) further characteristics about prime numbers. Furthermore, this engineering methodology can be scaled on Collatz conjecture in order to architect odd numbers according to converged trees where odd numbers are presented in form of distributed structures of terms, which may provide insights about prime numbers and their distribution.
Because the contained results in this article are original, consisting of many new codependent formulas, mathematical expressions and new theorems interconnected in a scaling manner basing on extendable logic; every proposed formula will be proved mathematically and used to build the rest of presented content, and we will scale through them by relying on logical analysis and deduction which are following a structured development architecture guided by the proposed engineering methodology in this paper.
This engineering methodology was first used to develop the solution of quartic polynomial equations in general forms
[27] | Larbaoui, Y. New Theorems and Formulas to Solve Fourth Degree Polynomial Equation in General Forms by Calculating the Four Roots Nearly Simultaneously. American Journal of Applied Mathematics. vol. 11(6): 95-105. |
[27]
, by building the unified formulas of the four roots of any quartic equation, which allow calculating the four solutions nearly simultaneously. Then, the same engineering methodology was scaled to solve quantic equations
[28] | Larbaoui, Y. New Theorems Solving Fifth Degree Polynomial Equation in Complete Forms by Proposing New Five Roots Composed of Radical Expressions. American Journal of Applied Mathematics. Vol2. 1: 9-23. |
[28]
in complete forms by proposing the necessary unified formulas of roots to calculate the five solutions nearly in parallel. Therefore, this paper is allowing to scale this engineering methodology from quartic and quantic polynomials toward solving sixth degree polynomial equations in general forms whereas enabling values calculation of all roots nearly in parallel.
The contents of this paper are structured as follow: Section 2 presenting the used methodology and its results of engineered requirements and techniques to solve polynomial equations of nth degree. Section 3 presenting four formulary solutions for fourth degree polynomial equations in general forms, which enable calculating the roots of these equations nearly in parallel. Section 4, presenting new six formulary solutions using radical expressions to solve sixth degree polynomial equation in general forms where the coefficient of fifth degree part is different from zero. Section 5, presenting new six roots solving sixth degree polynomial equation in general forms where the coefficient of fifth degree part is equal zero. Finally, Section 6 for conclusion.
2. Engineered Methodology and Techniques to Solve Nth Degree Polynomial Equations
The used methodology in this paper to solve nth degree polynomial equations in general forms is based on architecting roots according to a distributed structure of terms while relying on radicality.
In addition, this used methodology is relying on developing specific patterns into the structure of roots in order to help converging calculations whereas eliminating degrees.
Furthermore, this methodology is built on an engineering logic where roots are predesigned before being expressed according to unified formulas, which support the expressions structuring for all roots of polynomial equation.
The used methodology in this paper lead to define a list of engineered requirements and techniques, which are helping to develop the necessary unified formulas to calculate the roots of nth degree polynomial equations in general forms whereas enabling to calculate the values of possible roots nearly in parallel.
The results of our engineered requirements and techniques according to the used methodology are described as follow:
1. Roots should be expressed according to a distributed structure of terms

, which will be multiplied by each other during calculations.
2. Each included term in the distributed structure of roots should be expressed according to the simplest possible radicality.
3. All included terms in the distributed structure of roots should either be constants or be radical expressions.
4. The included constant terms in the distributed structure of roots should allow eliminating specific parts with specific degrees from a polynomial equation.
5. We adapt a polynomial equation of nth degree

where

by presenting it as

.
6. We use the expression

to eliminate the term of degree

from a polynomial equation of nth degree

when

is an odd value or when this elimination is simplifying calculations.
7. All included radical terms in each root should have the same radicality, in order to converge resulted expressions during calculations. Therefore, we choose them to have a radicality of square root.
8. Each included radical term in the distributed structure of a root

should be expressed according to a sum of simple radical terms

when the degree of polynomial equation is equal four.
9. Each included radical term in the distributed structure of a root

should be expressed according to a multiplication of at least two different sub-terms

when the degree of polynomial equation is surpassing four.
10. When the degree of polynomial equation is surpassing four, each included sub-term

in the distributed structure of a root

should appear in multiple distributed terms in order to allow further factorizations.
11. When the degree of polynomial equation is surpassing four, each included sub-term

in the distributed structure of terms

should be presented according to a radical expression of cubic root, quadratic root or a constant.
12. Combinations among included sub-terms in a root should allow expressing the values of involved coefficients in a polynomial equation.
13. The included sub-terms in the distributed structure of terms should allow neutralizing their contents when they are multiplied by each other in order to have simplified results.
14. The included sub-terms in the distributed structure of terms should allow eliminating radicality when they are raised to the power of higher polynomial degrees.
15. The included sub-terms in the distributed structure of terms should allow eliminating radicality when they are multiplied by each other.
16. The included sub-terms in the distributed structure of terms should allow forwarded calculations to supress terms that have odd values of polynomial degrees.
17. The included sub-terms in the distributed structure of terms should allow forwarded calculations to either supressing terms of the highest degrees or supressing terms of the lowest degrees.
18. The distributed structure of terms

should include a sub-term

presented according to a radical expression of cubic root where

.
19. The distributed structure of terms should include two sub-terms

presented according to radical expressions of quadratic roots where
and

.
20. In order to eliminate high degree expressions in a polynomial equation whereas allowing calculations to converge, we use a constant value

expressed by using included sub-terms in the distributed structure of root where

.
21. In order to eliminate average degree expressions in a polynomial equation whereas allowing calculations to converge, we use a constant value

expressed by using included sub-terms in the distributed structure of root where
22. In order to eliminate low degree expressions in a polynomial equation whereas allowing calculations to converge, we use a constant value

expressed by using included sub-terms in the distributed structure of root where
23. In order to eliminate the lowest degree expressions in a polynomial equation whereas allowing calculations to converge, we use a constant value

expressed by using included sub-terms in the distributed structure of root where

.
24. In order to eliminate odd degrees of expressions in a polynomial equation whereas allowing calculations to converge, we re-formulate the solution

to be presented as
. 25. In order to reduce degrees of expressions in a polynomial equation whereas allowing calculations to converge, we re-formulate the second-degree form

to be presented as
. 26. In order to reduce degrees of complex expressions in a polynomial equation whereas allowing calculations to converge, we re-formulate the quartic form

to be presented as
. 27. We use the proposed constants

and the expression

in order re-express the polynomial equation

to be represented as

where

.
28. When the solution of nth degree polynomial equation is expressed as
, we adopt a constant value

where

is expressed in function of
; in order to converge calculations during the process of equations solving.
29. The resulted polynomial expression at the final stages of forwarded calculations should have only one unknown variable expressed by including the use of one sub-term incorporated in the distributed structure of roots which to be considered as an unknown variable.
30. The resulted polynomial form at the final stages of forwarded calculations should have less degree than the staring point, or should not have the term of constant value (the term with zero degree). Otherwise, this resulted polynomial form should not have any terms with odd degrees.
31. The included sub-terms

in the distributed structure of a root

should also be used in the calculation of all other roots by changing signs of these sub-terms whereas exploiting the involved coefficients in the polynomial equation.
32. Reusing the included sub-terms in the structure of a root while only changing their signs should allow calculating the values of different roots

nearly in parallel.
3. Solutions and Theorems for Fourth Degree Polynomial Equation in General Form
This section presents new unified formulary solutions for fourth degree polynomial equation in general form.
3.1. First Proposed Theorem
In this subsection, we propose a new theorem to solve fourth degree polynomial equations that may be presented as shown in (eq.
1). The expressions of proposed solutions are dependent on the value of the expression

. We are proposing four solutions for

, four solutions for

and four solutions for

.
The proposed solutions are expressed by using

, which is presented in (eq.
17), and by using

,

and

shown in (eq.
6).
The proof of this theorem is presented in an independent subsection, because it is long and it contains the full expressions of proposed solutions along with details, in order to highlight the used logic to develop those solutions and to build the ground that we use to prove other proposed theorems in this paper.
Theorem 1
A fourth-degree polynomial equation under the expression (eq.
1), where coefficients belong to the group of numbers

, has four solutions:
(1) If

, and by using the expressions of

in (eq.
17), P in (Eq.
6) and Q in (Eq.
6):
a) Solution 1:

presented in the expression (eq.
35);
b) Solution 2:

presented in the expression (eq.
36);
c) Solution 3:

presented in the expression (eq.
37);
d) Solution 4:

presented in the expression (eq.
38).
If

, and by using the expressions of

in (eq.
17), P in (Eq.
6) and Q in (Eq.
6):
a) Solution 1:

presented in the expression (eq.
39);
b) Solution 2:

presented in the expression (eq.
40);
c) Solution 3:

presented in the expression (eq.
41);
d) Solution 4:

presented in the expression (eq.
42).
If

, and by using the expressions of

in (eq.
28), P in (Eq.
6) and Q in (Eq.
6):
a) Solution 1:

presented in the expression (eq.
43);
b) Solution 2:

presented in the expression (eq.
44);
c) Solution 3:

presented in the expression (eq.
45);
d) Solution 4:

presented in the expression (eq.
46).
3.2. Proof of Theorem 1
By dividing the polynomial (eq.
1) on the coefficient

, we have the next form:
(2) We suppose that

is expressed as shown in (eq.
3):
(3) We replace

with supposed expression in (eq.
3) to reduce the form of presented polynomial in (eq.
2). Thereby, we have the presented expression in (eq.
4).
(4) To simplify the expression of shown polynomial equation in (eq.
4), we replace the expressions of used coefficients as shown in (eq.
5) where the values of those coefficients are defined in (eq.
6).
(5)
(6) To solve the shown polynomial equation in (eq.
5), we propose new expressions for the variable

; expressions (eq.
7) and (eq.
8):
For
For

:
(7) For
For

:
(8) We propose the expressions (eq.
9) and (eq.
10) for

and

successively, in condition of

. Those expressions of

and

are based on quadratic solutions.
(9)
(10) To reduce the expression of equation (eq.
5) and find a way to solve it, we propose the following expressions for the coefficients

and

:
(11) For
For

:
(12) For
For

:
(13) In the following calculation, we replace the variable

with the expression (eq.
7) where we suppose

, and we replace P and Q with their shown expressions in (eq.
11) and (eq.
12):
(14) To solve the resulted expression in (eq.
14), we use Cardano’s solution for third degree polynomial equations.
For

, Cardano's solution is as follow:
(15) For

, we use the form

and we suppose

and

to express the cubic solution as follow:
(16) By using the expression (eq.
16), the solutions of third degree polynomial equation shown in (eq.
14) are

in (eq.
17),

in (eq.
18) and

in (eq.
19), where

,

and
(17) In condition of

,

and

are as follow:
(18)
(19) We deduce that when

takes the value

, the value of

is equal to the shown value of

in (eq.
9), and the value of

is equal to the shown value of

in (eq.
10).
There are three other possible expressions for

which respect the proposition

when

, and they give the same results of calculations toward having the shown third degree polynomial in (eq.
14). Thereby, they give the same values for roots

and

. These three expressions are

,

and

.
By using the expressions in (eq.
6) and (eq.
17), the solutions of presented fourth degree polynomial equation in (eq.
5) when

are as shown in (eq.
20), (eq.
21), (eq.
22) and (eq.
23).
Solution 1:
Solution 1:
(20) Solution 2:
Solution 2:
(21) Solution 3:
Solution 3:
(22) Solution 4:
Solution 4:
(23) There are three other possible expressions for

which respect the proposition

when

, and they give the same third degree polynomial shown in (eq.
14) after calculations. These three expressions are

,

and

.
By using the shown expressions in (eq.
6) and (eq.
17), the solutions of presented fourth degree polynomial equation in (eq.
5) when

are as shown in (eq.
24), (eq.
25), (eq.
26) and (eq.
27).
Solution 1:
Solution 1:
(24) Solution 2:
Solution 2:
(25) Solution 3:
Solution 3:
(26) Solution 4:
Solution 4:
(27) Concerning
Concerning
The expression of

is as shown in (eq.
28) where

and

, whereas

and

are as shown in (eq.
29) and (eq.
30).
(28)
(29)
(30) Because of having the expressions

or

, and having the intersection between the forms (eq.
7) and (eq.
8) for Q=0

, there are four solutions for the polynomial equation shown in (eq.
5) when Q=0 and they are as shown in (eq.
31), (eq.
32), (eq.
33) and (eq.
34).
Solution 1:
Solution 1:
(31) Solution 2:
Solution 2:
(32) Solution 3:
Solution 3:
(33) Solution 4:
Solution 4:
(34) When we give the value

in (eq.
17) to

, the values of

in (eq.
18) and

in (eq.
19) are equal to the shown values of

in (eq.
9) and (

in (eq.
10) respectively. Thereby, even when we replace the value of

in the expressions of proposed solutions by the values of

or

, the results are only redundancies of proposed solutions, because the value of

in the precedent expressions and in the proposed solutions is as follow:
In order to solve the polynomial equation shown in (eq.
2), we use the expression

where

is the unknown variable in polynomial equation (eq.
5). By using expressions (eq.
6) and (eq.
17) for

, the solutions for equation (eq.
1) are as shown in (eq.
35), (eq.
36), (eq.
37) and (eq.
38).
Solution 1:
Solution 1:
(35) Solution 2:
Solution 2:
(36) Solution 3:
Solution 3:
(37) Solution 4:
Solution 4:
(38) By using the expression

while relying on expressions (eq.
6) and (eq.
17) for

, the proposed solutions for equation (eq.
1) are as shown in (eq.
39), (eq.
40), (eq.
41) and (eq.
42).
Solution 1:
Solution 1:
(39) Solution 2:
Solution 2:
(40) Solution 3:
Solution 3:
(41) Solution 4:
Solution 4:
(42) By using the expression

while relying on expressions (eq.
6) and (eq.
28) for

, the proposed solutions for equation (eq.
1) are as shown in (eq.
43), (eq.
44), (eq.
45) and (eq.
46).
Solution 1:
Solution 1:
(43) Solution 2:
Solution 2:
(44) Solution 3:
Solution 3:
(45) Solution 4:
Solution 4:
(46) 4. New Six Solutions for Sixth Degree Polynomial Equation in General Form
In this section, we propose six new solutions for sixth degree polynomial equation in general form shown in (eq.
47), where we rely on our proposed solutions for quartic polynomial equations in previous section to structure the expressions of proposed solutions for sixth degree polynomial equations. We extend the used logic in precedent theorem (Theorem 1) by projection on sixth degree equations to prove the expressions of developed roots.
4.1. Second Proposed Theorem
In this subsection, we present our second proposed theorem to introduce new six formulary solutions for sixth degree polynomial equation in general form shown in (eq.
47), where coefficients belong to the group ℝ whereas the coefficient of fifth degree part is different from zero. First, we divide the polynomial (eq.
47) on coefficient A to reduce its expression to the simplified form shown in (eq.
48) where coefficients are expressed as shown in (eq.
49).
(47)
(48)
(49)
(50) Theorem 2
After reducing the form of sixth degree polynomial shown in (eq.
47) to the presented form in (eq.
48) where coefficients are as expressed in (eq.
49); the sixth-degree polynomial equation shown in (eq.
48), where coefficients belong to the group of numbers ℝ, can be reduced to a fourth-degree polynomial equation, which may be expressed as shown in (eq.
50). The reduction from sixth degree polynomial to quartic polynomial is conducted by supposing

, whereas supposing

is the solution for fourth degree polynomial equation in (eq.
50) by using Theorem 1 and relying on the expression

The variable

is defined as shown in (eq.
51) where

is presented in (eq.
52) and

is the solution for the polynomial equation (eq.
53), which relies on the coefficients (eq.
54), (eq.
55), (eq.
56) and (eq.
57). The shown coefficients in (eq.
54), (eq.
55), (eq.
56) and (eq.
57) are expressed by using the constant

which is presented in (eq.
58). The coefficients

,

,

and

of quartic equation (eq.
50), which is used to calculate

, are determined by using the shown expressions in (51), (eq.
59), (eq.
60) and (eq.
61) while using calculated values of

and

. As a result, we have twelve calculated values as potential solutions for sixth degree polynomial equation shown in (eq.
48), where many of them are only redundancies of others, because there are only six official solutions to determine.
The twelve solutions to calculate for sixth degree equation (eq.
48) are as shown in the groups (eq.
99), (eq.
100) and (eq.
101). The proposed six values as official solutions for sixth degree polynomial equation shown in (eq.
48) are as presented in (eq.
102), (eq.
103), (eq.
104), (eq.
105), (eq.
106) and (eq.
107).
(51)
(52)
(53)
(54)
(55)
(56)
(57)
(58)
(59)
(60)
(61) 4.2. Proof of Theorem 2
Considering the sixth-degree polynomial equation shown in (eq.
48), we propose the expression (eq.
62) in order to reduce the form from sixth degree to a fourth-degree polynomial. We also propose the expression (eq.
63), which presents the solution form for quartic equation by extending the used logic and presented solutions in Theorem 1.
(62)
(63) We replace

with its proposed value in (eq.
62), in order to end by calculations to the reduced form shown in (eq.
50).
In the shown expressions in (eq.
64), we rely on the use of

,

and

where

and

.
(64)
(65)
(66)
(67)
(68)
(69)
(70)
(71) We use the expressions of

in (eq.
64),

in (eq.
65),

in (eq.
66),

in (eq.
67),

in (eq.
68),

in (eq.
69) and

in (eq.
70), to have the fourth degree polynomial shown in (eq.
71) where the values of coefficients are as follow:
We divide the polynomial equation shown in (eq.
71) on

to simplify its expression. As a result, we have the shown equation in (eq.
50) where the values of coefficients are as follow:
From precedent section (section 2), we ended with solutions expressed as

for fourth degree polynomial equation in simple form shown in (eq.
5), whereas the solution for fourth degree polynomial equation in complete form is expressed as

.
We replace

with

in order to reduce the form of quartic equation from expression (eq.
50) to expression (eq.
72), where the values of coefficients are as shown in (eq.
73).
(72)
(73) Concerning the fourth degree polynomial equation in (eq.
50), where

is as shown in (eq.
63), the principal proposed expressions for the solutions are

when

and

; where

and

. These two principal expressions are sufficient to conduct the calculations of proof, and then generalize the results by using the other expressed forms of solutions in Theorem 1.
We replace

with their values in function of

in order to have the expressions of

in (eq.
74),

in (eq.
75) and

in (eq.
76).
(74)
(75) By using the expressions (eq.
11), (eq.
12), (eq.
13) and (eq.
14) from the proof of first proposed theorem (Theorem 1), the values of

,

and

are as shown in (eq.
77), (eq.
78) and (eq.
79) successively.
(77)
(78)
(79) We have a group of four variables

, whereas we have a group of only three equations to solve

where all of them are dependent on the value of

. Thereby, the next step is about using the appropriate logic of analysis and calculation to find the value of

while taking advantage of the fact that having a group of four variables enables us to solve four equations.
In order to reduce the expression of

in (eq.
76), and find a way to determine the value of

, we suppose that

where

. As a result, we have the shown expression in (eq.
80).
(80) From expression (eq.
80), we can see that

has a constant value. Therefore, in the rest of calculation, we will replace

by the constant

, which is shown in (eq.
58).
From precedent calculations of dividing the polynomial equation shown in (eq.
71) on

to simplify its expression, along using the expression of

, we have

.
We have the resulted equation in (eq.
81) by using the expressions of

in (eq.
74) and (eq.
77), which we use to define the shown value of

in (eq.
82).
(81)
(82) We have the presented polynomial equation in (eq.
83) by using the expressions of

in (eq.
76) and (eq.
79).
(83) We replace

with its shown expression in (eq.
80) to pass from equation (eq.
83) to equation (eq.
84).
(84) We use equations (eq.
75) and (eq.
78) to calculate the value of

and then express

as shown in (eq.
85) where we rely on replacing

with its constant value

, which is presented in (eq.
80).
(85) In order to pass from equation (eq.
84) to equation (eq.
86), we replace
In order to pass from equation (eq.
84) to equation (eq.
86), we replace

with its shown expression in (eq.
85).
(86) We replace

with its shown expression in (eq.
82), and then we assemble terms of equation (eq.
86) in function of degrees, in order to have the expression (eq.
88) where coefficients are presented in (eq.
54), (eq.
55), (eq.
56) and (eq.
57).
(87)
(88) Since we supposed that

whereas adopting

, we eliminate the root zero as solution for polynomial equation (eq.
88) and we use the cubic solution to solve the polynomial equation

, because all coefficients are expressed only in function of

,

,

,

,

and the constant

. As a result, we have six possible values for

as solutions for polynomial equation shown in (eq.
53).
Supposing that

is the group of solutions for shown equation in (eq.
53), where these solutions are expressed as

and

with

. The group of solutions

is determined by relying on cubic root shown in (eq.
90) and quadratic roots (eq.
91) and (eq.
92).
(89) We suppose that

,

and

, whereas using the expressions (eq.
54), (eq.
55), (eq.
56) and (eq.
57). We suppose also that

and

. The solutions

,

and

for shown equation in (eq.
53) are as follow:
(90)
(91)
(92) After determining the values of

by using cubic solution and quadratic solutions, the following step consists of solving the polynomial equation shown in (eq.
72).
The coefficients

in (eq.
74) and

in (eq.
76) are dependent on

and

. The coefficient

in (eq.
82) is dependent on

, whereas the coefficient

shown in (eq.
75) is dependent on

and

. Therefore, we are going to use only

,

and

to calculate the potential values of

because

are going only to inverse the sign of coefficient

and thereby inversing the signs of potential values of

as solutions for polynomial equation shown in (eq.
50), which will not influence the potential values of

as solutions for sixth degree polynomial equation shown in (eq.
48) because
We use the first proposed theorem (Theorem 1) to calculate the four solutions for fourth degree polynomial equation shown in (eq.
72) after calculating the coefficients

,

and

for each value of

from the group

. Thereby, we have twelve values to calculate as potential solutions for the polynomial equation shown in (eq.
72).
After using first proposed theorem on (eq.
72) for each value of

from the group

, we have three groups of potential solutions for polynomial equation shown in (eq.
72), where each group is dependent on different value of

. We express these groups of solutions as follow:

.
(93)
(94)
(95) Concerning the fourth-degree polynomial equation shown in (eq.
50), we have three groups of solutions where each group is dependent on different value of

; as shown in (eq.
96), (eq.
97) and (eq.
98). The values of

, where

and

, are from the expressed solutions in the groups (eq.
93), (eq.
94) and (eq.
95).
(96)
(97)
(98) We suppose that

where

and

, in order to simplify the expressed values in (eq.
96), (eq.
97) and (eq.
98). Thereby, we have three groups of values as potential solutions for sixth degree polynomial equation shown in (eq.
48). These three groups are as shown in (eq.
99), (eq.
100) and (eq.
101) where

is as follow:
The expression of

is an extending of the shown expression of

in (eq.
82) by changing the value of

, where

belong to the group

.
(99)
(100)
(101) We have twelve values as potential solutions for the sixth degree polynomial equation shown in (eq.
48). However, many of them are only redundancies of others and there are only six official solutions to determine. The variables

are the responsible of solution redundancies from one group to other.
In order to avoid the complications of calculating the twelve values from the groups

,

and

, and then determining the six solutions for sixth degree polynomial equation shown in (eq.
48), we propose the expressed values in (eq.
102), (eq.
103), (eq.
104), (eq.
105), (eq.
106) and (eq.
107) as the six official solutions for sixth degree polynomial equation shown in (eq.
48).
The first four proposed values as solutions for sixth degree polynomial equation shown in (eq.
48) are from the group

, whereas the fifth and sixth values are expressed by deduction using the expressions of quadratic roots. The useless redundancies of solutions are from one group to other; therefore, we choose the first four solutions from the same group

.
In our six proposed solutions, we use the values

where

and

from

. The variable

is expressed as follow:

is from the group

shown in (eq.
88) which contains the solutions for polynomial equation (eq.
52). The values of

, where

, are the solutions for quartic equation (eq.
50) and they are determined by using Theorem 1.
(102)
(103)
(104)
(105)
(106)
(107) 4.3. Third Proposed Theorem
In the second proposed theorem in this paper, we rely on reducing sixth degree polynomial equation to fourth degree in order to find proper roots for concerned equation. However, the fourth degree part of resulted quartic equation by reduction is dependent on the fifth degree part of concerned sixth degree polynomial. Thereby, the equation

where the coefficient of fifth degree part is equal zero imposes a problem of reduction to fourth degree.
Therefore, in this subsection, we present a third theorem to propose six formulary solutions for sixth degree polynomial equation in general form

, where coefficients belong to the group of numbers ℝ and the coefficient of fifth degree part equal zero.
This third proposed theorem is based on the same logic and calculations of Theorem 2. However, it is distinguished by treating sixth degree polynomial where the fifth degree part is absent. First, we pass from equation expression

to the expression

, and then we use the expression

to induce a fifth degree part whereas eliminating the fourth degree part of concerned sixth degree polynomial.
Inducing the fifth degree part in polynomial equation shown in (eq.
108), whereas eliminating the fourth degree part; help to reduce the amount of calculations comparing to the situation of having a fourth degree element to treat during the process of reduction from sixth degree polynomial equation to quartic equation.
The shown equation in (eq.
108) is resulted by replacing

with

. The coefficients of equation (eq.
108) are as expressed in (eq.
109), (eq.
110), (eq.
111), (eq.
112) and (eq.
113).
(108)
(109)
(110)
(111)
(112)
(113) Theorem 3
In order to reduce the sixth degree polynomial equation

to the quartic equation shown in (eq.
114), where coefficients belong to the group of numbers ℝ we first replace

with

Then, the reduction from sixth degree to fourth degree is conducted by supposing

, whereas supposing

is the solution for fourth degree polynomial equation in (eq.
114) by using Theorem 1 and relying on the expression

. The variable

is defined as shown in (eq.
115) where

is presented in (eq.
119) and

is the solution for the polynomial equation (eq.
120), which relies on the coefficients (eq.
121), (eq.
122), (eq.
123) and (eq.
124). The shown coefficients in (eq.
121), (eq.
122), (eq.
123) and (eq.
124) are expressed by using the constant

, which is defined in (eq.
125). The coefficients

,

,

and

of quartic equation (eq.
114) are determined by using calculated value of

and using the shown expressions in (eq.
115), (eq.
116), (eq.
117) and (eq.
118). The six proposed solutions for polynomial equation

are as shown in (eq.
136), (eq.
137), (eq.
138), (eq.
139), (140) and (eq.
141).
(114)
(115)
(116)
(117)
(118)
(119)
(120)
(121)
(122)
(123)
(124)
(125) 4.4. Proof of Theorem 3
Considering the sixth-degree polynomial equation

where the fifth degree part is absent, we divide the polynomial on

and then we use the expression

in order to induce a fifth degree part and eliminate the fourth degree part. Then, by using the expression (eq.
62), we reduce the resulted sixth degree polynomial (eq.
108) to the quartic polynomial shown in (eq.
126).
(126) We rely on the expressions of

in (eq.
64),

in (eq.
65),

in (eq.
66),

in (eq.
67),

in (eq.
69) and

in (eq.
70) to express the fourth degree polynomial shown in (eq.
126) where the values of coefficients are as follow:
We have the shown fourth degree polynomial in (eq.
114) after dividing the polynomial (eq.
126) on

. The coefficients of polynomial (eq.
114) are as follow:
We have the fourth degree polynomial

by replacing

with

in the polynomial (eq.
114). The coefficients

,

and

are as expressed in (eq.
127), (eq.
128) and (eq.
129).
(127)
(128)
(129) In order to reduce the expression of

in (eq.
129), and find a way to determine the value of

, we suppose that

where

. As a result, we have the shown expression in (eq.
130).
(130) We rely on the same used logic and processes of calculation in the proof of Theorem 2, in order to continue the proof of third proposed theorem. Thereby, the variables

,

and

are as expressed in (eq.
131), (eq.
132) and (eq.
133) respectively, whereas the resulted polynomial equation to determine the value of

is as shown in (eq.
134).
(131)
(132)
(133)
(134) We use the shown value of

in (eq.
130) and we replace

and

with their shown expressions in (eq.
131) and (eq.
133), in order to pass from equation (eq.
134) to polynomial expression

where coefficients are as presented in (eq.
121), (eq.
122), (eq.
123) and (eq.
124).
Relying on the proof of Theorem 2, we calculate only the expression

shown in (eq.
135) as a root for expressed equation in (eq.
120), and then we determine the roots of quartic equation

. Therefore, we start by calculating the values of

,

and

by replacing the variable

with the value of

, then we calculate the values of

,

and

, and finally we finish by using Theorem 1.
We suppose that

and

, whereas using the expressions (eq.
121), (eq.
122), (eq.
123) and (eq.
124). We suppose also that

and

. The solution

for shown equation in (eq.
120) is as follow:
(135) As we mentioned in the proof of Theorem 2, the use of other roots of polynomial (eq.
120) in the quartic polynomial

to calculate the values of

,

and

generates redundancies of roots for the sixth degree polynomial equation

.
We determine the group

, which contains the four roots for quartic equation

, by using Theorem 1.
We present the group of roots for quartic equation shown in (eq.
114) as

, which is determined by relying on the group

.
We present each root for quartic equation shown in (eq.
114) as

, whereas

is from the group

.
The proposed six solutions for sixth degree polynomial equation

are as expressed in (eq.
136), (eq.
137), (eq.
138), (eq.
139), (140) and (eq.
141). The expressions

,

,

and

present the calculated roots for quartic equation (eq.
114) by using Theorem 1.

is calculated by using the shown expression in (eq.
135). We use the expression (eq.
131) to calculate the value of

; thereby, its value is as follow:
(136)
(137)
(138)
(139)
(140)
(141)