8x^2-9x-120=0

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Solution for 8x^2-9x-120=0 equation:


Simplifying
8x2 + -9x + -120 = 0

Reorder the terms:
-120 + -9x + 8x2 = 0

Solving
-120 + -9x + 8x2 = 0

Solving for variable 'x'.

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

Divide each side by '8'.
-15 + -1.125x + x2 = 0

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -1.125x + 15 + x2 = 0 + 15

Reorder the terms:
-15 + 15 + -1.125x + x2 = 0 + 15

Combine like terms: -15 + 15 = 0
0 + -1.125x + x2 = 0 + 15
-1.125x + x2 = 0 + 15

Combine like terms: 0 + 15 = 15
-1.125x + x2 = 15

The x term is -1.125x.  Take half its coefficient (-0.5625).
Square it (0.31640625) and add it to both sides.

Add '0.31640625' to each side of the equation.
-1.125x + 0.31640625 + x2 = 15 + 0.31640625

Reorder the terms:
0.31640625 + -1.125x + x2 = 15 + 0.31640625

Combine like terms: 15 + 0.31640625 = 15.31640625
0.31640625 + -1.125x + x2 = 15.31640625

Factor a perfect square on the left side:
(x + -0.5625)(x + -0.5625) = 15.31640625

Calculate the square root of the right side: 3.913618051

Break this problem into two subproblems by setting 
(x + -0.5625) equal to 3.913618051 and -3.913618051.

Subproblem 1

x + -0.5625 = 3.913618051 Simplifying x + -0.5625 = 3.913618051 Reorder the terms: -0.5625 + x = 3.913618051 Solving -0.5625 + x = 3.913618051 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5625' to each side of the equation. -0.5625 + 0.5625 + x = 3.913618051 + 0.5625 Combine like terms: -0.5625 + 0.5625 = 0.0000 0.0000 + x = 3.913618051 + 0.5625 x = 3.913618051 + 0.5625 Combine like terms: 3.913618051 + 0.5625 = 4.476118051 x = 4.476118051 Simplifying x = 4.476118051

Subproblem 2

x + -0.5625 = -3.913618051 Simplifying x + -0.5625 = -3.913618051 Reorder the terms: -0.5625 + x = -3.913618051 Solving -0.5625 + x = -3.913618051 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.5625' to each side of the equation. -0.5625 + 0.5625 + x = -3.913618051 + 0.5625 Combine like terms: -0.5625 + 0.5625 = 0.0000 0.0000 + x = -3.913618051 + 0.5625 x = -3.913618051 + 0.5625 Combine like terms: -3.913618051 + 0.5625 = -3.351118051 x = -3.351118051 Simplifying x = -3.351118051

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.476118051, -3.351118051}

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