8x^2-5x-120=0

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Solution for 8x^2-5x-120=0 equation:


Simplifying
8x2 + -5x + -120 = 0

Reorder the terms:
-120 + -5x + 8x2 = 0

Solving
-120 + -5x + 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 + -0.625x + x2 = 0

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -0.625x + 15 + x2 = 0 + 15

Reorder the terms:
-15 + 15 + -0.625x + x2 = 0 + 15

Combine like terms: -15 + 15 = 0
0 + -0.625x + x2 = 0 + 15
-0.625x + x2 = 0 + 15

Combine like terms: 0 + 15 = 15
-0.625x + x2 = 15

The x term is -0.625x.  Take half its coefficient (-0.3125).
Square it (0.09765625) and add it to both sides.

Add '0.09765625' to each side of the equation.
-0.625x + 0.09765625 + x2 = 15 + 0.09765625

Reorder the terms:
0.09765625 + -0.625x + x2 = 15 + 0.09765625

Combine like terms: 15 + 0.09765625 = 15.09765625
0.09765625 + -0.625x + x2 = 15.09765625

Factor a perfect square on the left side:
(x + -0.3125)(x + -0.3125) = 15.09765625

Calculate the square root of the right side: 3.885570261

Break this problem into two subproblems by setting 
(x + -0.3125) equal to 3.885570261 and -3.885570261.

Subproblem 1

x + -0.3125 = 3.885570261 Simplifying x + -0.3125 = 3.885570261 Reorder the terms: -0.3125 + x = 3.885570261 Solving -0.3125 + x = 3.885570261 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.3125' to each side of the equation. -0.3125 + 0.3125 + x = 3.885570261 + 0.3125 Combine like terms: -0.3125 + 0.3125 = 0.0000 0.0000 + x = 3.885570261 + 0.3125 x = 3.885570261 + 0.3125 Combine like terms: 3.885570261 + 0.3125 = 4.198070261 x = 4.198070261 Simplifying x = 4.198070261

Subproblem 2

x + -0.3125 = -3.885570261 Simplifying x + -0.3125 = -3.885570261 Reorder the terms: -0.3125 + x = -3.885570261 Solving -0.3125 + x = -3.885570261 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.3125' to each side of the equation. -0.3125 + 0.3125 + x = -3.885570261 + 0.3125 Combine like terms: -0.3125 + 0.3125 = 0.0000 0.0000 + x = -3.885570261 + 0.3125 x = -3.885570261 + 0.3125 Combine like terms: -3.885570261 + 0.3125 = -3.573070261 x = -3.573070261 Simplifying x = -3.573070261

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.198070261, -3.573070261}

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