x^2-21x-108=0

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Solution for x^2-21x-108=0 equation:


Simplifying
x2 + -21x + -108 = 0

Reorder the terms:
-108 + -21x + x2 = 0

Solving
-108 + -21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '108' to each side of the equation.
-108 + -21x + 108 + x2 = 0 + 108

Reorder the terms:
-108 + 108 + -21x + x2 = 0 + 108

Combine like terms: -108 + 108 = 0
0 + -21x + x2 = 0 + 108
-21x + x2 = 0 + 108

Combine like terms: 0 + 108 = 108
-21x + x2 = 108

The x term is -21x.  Take half its coefficient (-10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
-21x + 110.25 + x2 = 108 + 110.25

Reorder the terms:
110.25 + -21x + x2 = 108 + 110.25

Combine like terms: 108 + 110.25 = 218.25
110.25 + -21x + x2 = 218.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 218.25

Calculate the square root of the right side: 14.773286703

Break this problem into two subproblems by setting 
(x + -10.5) equal to 14.773286703 and -14.773286703.

Subproblem 1

x + -10.5 = 14.773286703 Simplifying x + -10.5 = 14.773286703 Reorder the terms: -10.5 + x = 14.773286703 Solving -10.5 + x = 14.773286703 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = 14.773286703 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 14.773286703 + 10.5 x = 14.773286703 + 10.5 Combine like terms: 14.773286703 + 10.5 = 25.273286703 x = 25.273286703 Simplifying x = 25.273286703

Subproblem 2

x + -10.5 = -14.773286703 Simplifying x + -10.5 = -14.773286703 Reorder the terms: -10.5 + x = -14.773286703 Solving -10.5 + x = -14.773286703 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = -14.773286703 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -14.773286703 + 10.5 x = -14.773286703 + 10.5 Combine like terms: -14.773286703 + 10.5 = -4.273286703 x = -4.273286703 Simplifying x = -4.273286703

Solution

The solution to the problem is based on the solutions from the subproblems. x = {25.273286703, -4.273286703}

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