x^2+21x-115=0

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Solution for x^2+21x-115=0 equation:


Simplifying
x2 + 21x + -115 = 0

Reorder the terms:
-115 + 21x + x2 = 0

Solving
-115 + 21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '115' to each side of the equation.
-115 + 21x + 115 + x2 = 0 + 115

Reorder the terms:
-115 + 115 + 21x + x2 = 0 + 115

Combine like terms: -115 + 115 = 0
0 + 21x + x2 = 0 + 115
21x + x2 = 0 + 115

Combine like terms: 0 + 115 = 115
21x + x2 = 115

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 = 115 + 110.25

Reorder the terms:
110.25 + 21x + x2 = 115 + 110.25

Combine like terms: 115 + 110.25 = 225.25
110.25 + 21x + x2 = 225.25

Factor a perfect square on the left side:
(x + 10.5)(x + 10.5) = 225.25

Calculate the square root of the right side: 15.00833102

Break this problem into two subproblems by setting 
(x + 10.5) equal to 15.00833102 and -15.00833102.

Subproblem 1

x + 10.5 = 15.00833102 Simplifying x + 10.5 = 15.00833102 Reorder the terms: 10.5 + x = 15.00833102 Solving 10.5 + x = 15.00833102 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 = 15.00833102 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = 15.00833102 + -10.5 x = 15.00833102 + -10.5 Combine like terms: 15.00833102 + -10.5 = 4.50833102 x = 4.50833102 Simplifying x = 4.50833102

Subproblem 2

x + 10.5 = -15.00833102 Simplifying x + 10.5 = -15.00833102 Reorder the terms: 10.5 + x = -15.00833102 Solving 10.5 + x = -15.00833102 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 = -15.00833102 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = -15.00833102 + -10.5 x = -15.00833102 + -10.5 Combine like terms: -15.00833102 + -10.5 = -25.50833102 x = -25.50833102 Simplifying x = -25.50833102

Solution

The solution to the problem is based on the solutions from the subproblems. x = {4.50833102, -25.50833102}

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