-120=-5x^2-8x

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Solution for -120=-5x^2-8x equation:


Simplifying
-120 = -5x2 + -8x

Reorder the terms:
-120 = -8x + -5x2

Solving
-120 = -8x + -5x2

Solving for variable 'x'.

Reorder the terms:
-120 + 8x + 5x2 = -8x + 8x + -5x2 + 5x2

Combine like terms: -8x + 8x = 0
-120 + 8x + 5x2 = 0 + -5x2 + 5x2
-120 + 8x + 5x2 = -5x2 + 5x2

Combine like terms: -5x2 + 5x2 = 0
-120 + 8x + 5x2 = 0

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

Divide each side by '5'.
-24 + 1.6x + x2 = 0

Move the constant term to the right:

Add '24' to each side of the equation.
-24 + 1.6x + 24 + x2 = 0 + 24

Reorder the terms:
-24 + 24 + 1.6x + x2 = 0 + 24

Combine like terms: -24 + 24 = 0
0 + 1.6x + x2 = 0 + 24
1.6x + x2 = 0 + 24

Combine like terms: 0 + 24 = 24
1.6x + x2 = 24

The x term is 1.6x.  Take half its coefficient (0.8).
Square it (0.64) and add it to both sides.

Add '0.64' to each side of the equation.
1.6x + 0.64 + x2 = 24 + 0.64

Reorder the terms:
0.64 + 1.6x + x2 = 24 + 0.64

Combine like terms: 24 + 0.64 = 24.64
0.64 + 1.6x + x2 = 24.64

Factor a perfect square on the left side:
(x + 0.8)(x + 0.8) = 24.64

Calculate the square root of the right side: 4.963869458

Break this problem into two subproblems by setting 
(x + 0.8) equal to 4.963869458 and -4.963869458.

Subproblem 1

x + 0.8 = 4.963869458 Simplifying x + 0.8 = 4.963869458 Reorder the terms: 0.8 + x = 4.963869458 Solving 0.8 + x = 4.963869458 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8' to each side of the equation. 0.8 + -0.8 + x = 4.963869458 + -0.8 Combine like terms: 0.8 + -0.8 = 0.0 0.0 + x = 4.963869458 + -0.8 x = 4.963869458 + -0.8 Combine like terms: 4.963869458 + -0.8 = 4.163869458 x = 4.163869458 Simplifying x = 4.163869458

Subproblem 2

x + 0.8 = -4.963869458 Simplifying x + 0.8 = -4.963869458 Reorder the terms: 0.8 + x = -4.963869458 Solving 0.8 + x = -4.963869458 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-0.8' to each side of the equation. 0.8 + -0.8 + x = -4.963869458 + -0.8 Combine like terms: 0.8 + -0.8 = 0.0 0.0 + x = -4.963869458 + -0.8 x = -4.963869458 + -0.8 Combine like terms: -4.963869458 + -0.8 = -5.763869458 x = -5.763869458 Simplifying x = -5.763869458

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.163869458, -5.763869458}

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