x^2-15x-120=0

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Solution for x^2-15x-120=0 equation:


Simplifying
x2 + -15x + -120 = 0

Reorder the terms:
-120 + -15x + x2 = 0

Solving
-120 + -15x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '120' to each side of the equation.
-120 + -15x + 120 + x2 = 0 + 120

Reorder the terms:
-120 + 120 + -15x + x2 = 0 + 120

Combine like terms: -120 + 120 = 0
0 + -15x + x2 = 0 + 120
-15x + x2 = 0 + 120

Combine like terms: 0 + 120 = 120
-15x + x2 = 120

The x term is -15x.  Take half its coefficient (-7.5).
Square it (56.25) and add it to both sides.

Add '56.25' to each side of the equation.
-15x + 56.25 + x2 = 120 + 56.25

Reorder the terms:
56.25 + -15x + x2 = 120 + 56.25

Combine like terms: 120 + 56.25 = 176.25
56.25 + -15x + x2 = 176.25

Factor a perfect square on the left side:
(x + -7.5)(x + -7.5) = 176.25

Calculate the square root of the right side: 13.275918047

Break this problem into two subproblems by setting 
(x + -7.5) equal to 13.275918047 and -13.275918047.

Subproblem 1

x + -7.5 = 13.275918047 Simplifying x + -7.5 = 13.275918047 Reorder the terms: -7.5 + x = 13.275918047 Solving -7.5 + x = 13.275918047 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + x = 13.275918047 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = 13.275918047 + 7.5 x = 13.275918047 + 7.5 Combine like terms: 13.275918047 + 7.5 = 20.775918047 x = 20.775918047 Simplifying x = 20.775918047

Subproblem 2

x + -7.5 = -13.275918047 Simplifying x + -7.5 = -13.275918047 Reorder the terms: -7.5 + x = -13.275918047 Solving -7.5 + x = -13.275918047 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '7.5' to each side of the equation. -7.5 + 7.5 + x = -13.275918047 + 7.5 Combine like terms: -7.5 + 7.5 = 0.0 0.0 + x = -13.275918047 + 7.5 x = -13.275918047 + 7.5 Combine like terms: -13.275918047 + 7.5 = -5.775918047 x = -5.775918047 Simplifying x = -5.775918047

Solution

The solution to the problem is based on the solutions from the subproblems. x = {20.775918047, -5.775918047}

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