8x^2-7x-120=0

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Solution for 8x^2-7x-120=0 equation:


Simplifying
8x2 + -7x + -120 = 0

Reorder the terms:
-120 + -7x + 8x2 = 0

Solving
-120 + -7x + 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 + -0.875x + x2 = 0

Move the constant term to the right:

Add '15' to each side of the equation.
-15 + -0.875x + 15 + x2 = 0 + 15

Reorder the terms:
-15 + 15 + -0.875x + x2 = 0 + 15

Combine like terms: -15 + 15 = 0
0 + -0.875x + x2 = 0 + 15
-0.875x + x2 = 0 + 15

Combine like terms: 0 + 15 = 15
-0.875x + x2 = 15

The x term is -0.875x.  Take half its coefficient (-0.4375).
Square it (0.19140625) and add it to both sides.

Add '0.19140625' to each side of the equation.
-0.875x + 0.19140625 + x2 = 15 + 0.19140625

Reorder the terms:
0.19140625 + -0.875x + x2 = 15 + 0.19140625

Combine like terms: 15 + 0.19140625 = 15.19140625
0.19140625 + -0.875x + x2 = 15.19140625

Factor a perfect square on the left side:
(x + -0.4375)(x + -0.4375) = 15.19140625

Calculate the square root of the right side: 3.897615457

Break this problem into two subproblems by setting 
(x + -0.4375) equal to 3.897615457 and -3.897615457.

Subproblem 1

x + -0.4375 = 3.897615457 Simplifying x + -0.4375 = 3.897615457 Reorder the terms: -0.4375 + x = 3.897615457 Solving -0.4375 + x = 3.897615457 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.4375' to each side of the equation. -0.4375 + 0.4375 + x = 3.897615457 + 0.4375 Combine like terms: -0.4375 + 0.4375 = 0.0000 0.0000 + x = 3.897615457 + 0.4375 x = 3.897615457 + 0.4375 Combine like terms: 3.897615457 + 0.4375 = 4.335115457 x = 4.335115457 Simplifying x = 4.335115457

Subproblem 2

x + -0.4375 = -3.897615457 Simplifying x + -0.4375 = -3.897615457 Reorder the terms: -0.4375 + x = -3.897615457 Solving -0.4375 + x = -3.897615457 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '0.4375' to each side of the equation. -0.4375 + 0.4375 + x = -3.897615457 + 0.4375 Combine like terms: -0.4375 + 0.4375 = 0.0000 0.0000 + x = -3.897615457 + 0.4375 x = -3.897615457 + 0.4375 Combine like terms: -3.897615457 + 0.4375 = -3.460115457 x = -3.460115457 Simplifying x = -3.460115457

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.335115457, -3.460115457}

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