x=3x^2-7x-20

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Solution for x=3x^2-7x-20 equation:


Simplifying
x = 3x2 + -7x + -20

Reorder the terms:
x = -20 + -7x + 3x2

Solving
x = -20 + -7x + 3x2

Solving for variable 'x'.

Reorder the terms:
20 + x + 7x + -3x2 = -20 + -7x + 3x2 + 20 + 7x + -3x2

Combine like terms: x + 7x = 8x
20 + 8x + -3x2 = -20 + -7x + 3x2 + 20 + 7x + -3x2

Reorder the terms:
20 + 8x + -3x2 = -20 + 20 + -7x + 7x + 3x2 + -3x2

Combine like terms: -20 + 20 = 0
20 + 8x + -3x2 = 0 + -7x + 7x + 3x2 + -3x2
20 + 8x + -3x2 = -7x + 7x + 3x2 + -3x2

Combine like terms: -7x + 7x = 0
20 + 8x + -3x2 = 0 + 3x2 + -3x2
20 + 8x + -3x2 = 3x2 + -3x2

Combine like terms: 3x2 + -3x2 = 0
20 + 8x + -3x2 = 0

Begin completing the square.  Divide all terms by
-3 the coefficient of the squared term: 

Divide each side by '-3'.
-6.666666667 + -2.666666667x + x2 = 0

Move the constant term to the right:

Add '6.666666667' to each side of the equation.
-6.666666667 + -2.666666667x + 6.666666667 + x2 = 0 + 6.666666667

Reorder the terms:
-6.666666667 + 6.666666667 + -2.666666667x + x2 = 0 + 6.666666667

Combine like terms: -6.666666667 + 6.666666667 = 0.000000000
0.000000000 + -2.666666667x + x2 = 0 + 6.666666667
-2.666666667x + x2 = 0 + 6.666666667

Combine like terms: 0 + 6.666666667 = 6.666666667
-2.666666667x + x2 = 6.666666667

The x term is -2.666666667x.  Take half its coefficient (-1.333333334).
Square it (1.777777780) and add it to both sides.

Add '1.777777780' to each side of the equation.
-2.666666667x + 1.777777780 + x2 = 6.666666667 + 1.777777780

Reorder the terms:
1.777777780 + -2.666666667x + x2 = 6.666666667 + 1.777777780

Combine like terms: 6.666666667 + 1.777777780 = 8.444444447
1.777777780 + -2.666666667x + x2 = 8.444444447

Factor a perfect square on the left side:
(x + -1.333333334)(x + -1.333333334) = 8.444444447

Calculate the square root of the right side: 2.905932629

Break this problem into two subproblems by setting 
(x + -1.333333334) equal to 2.905932629 and -2.905932629.

Subproblem 1

x + -1.333333334 = 2.905932629 Simplifying x + -1.333333334 = 2.905932629 Reorder the terms: -1.333333334 + x = 2.905932629 Solving -1.333333334 + x = 2.905932629 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.333333334' to each side of the equation. -1.333333334 + 1.333333334 + x = 2.905932629 + 1.333333334 Combine like terms: -1.333333334 + 1.333333334 = 0.000000000 0.000000000 + x = 2.905932629 + 1.333333334 x = 2.905932629 + 1.333333334 Combine like terms: 2.905932629 + 1.333333334 = 4.239265963 x = 4.239265963 Simplifying x = 4.239265963

Subproblem 2

x + -1.333333334 = -2.905932629 Simplifying x + -1.333333334 = -2.905932629 Reorder the terms: -1.333333334 + x = -2.905932629 Solving -1.333333334 + x = -2.905932629 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.333333334' to each side of the equation. -1.333333334 + 1.333333334 + x = -2.905932629 + 1.333333334 Combine like terms: -1.333333334 + 1.333333334 = 0.000000000 0.000000000 + x = -2.905932629 + 1.333333334 x = -2.905932629 + 1.333333334 Combine like terms: -2.905932629 + 1.333333334 = -1.572599295 x = -1.572599295 Simplifying x = -1.572599295

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.239265963, -1.572599295}

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