x^2+12x-15=21

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Solution for x^2+12x-15=21 equation:


Simplifying
x2 + 12x + -15 = 21

Reorder the terms:
-15 + 12x + x2 = 21

Solving
-15 + 12x + x2 = 21

Solving for variable 'x'.

Reorder the terms:
-15 + -21 + 12x + x2 = 21 + -21

Combine like terms: -15 + -21 = -36
-36 + 12x + x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-36 + 12x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '36' to each side of the equation.
-36 + 12x + 36 + x2 = 0 + 36

Reorder the terms:
-36 + 36 + 12x + x2 = 0 + 36

Combine like terms: -36 + 36 = 0
0 + 12x + x2 = 0 + 36
12x + x2 = 0 + 36

Combine like terms: 0 + 36 = 36
12x + x2 = 36

The x term is 12x.  Take half its coefficient (6).
Square it (36) and add it to both sides.

Add '36' to each side of the equation.
12x + 36 + x2 = 36 + 36

Reorder the terms:
36 + 12x + x2 = 36 + 36

Combine like terms: 36 + 36 = 72
36 + 12x + x2 = 72

Factor a perfect square on the left side:
(x + 6)(x + 6) = 72

Calculate the square root of the right side: 8.485281374

Break this problem into two subproblems by setting 
(x + 6) equal to 8.485281374 and -8.485281374.

Subproblem 1

x + 6 = 8.485281374 Simplifying x + 6 = 8.485281374 Reorder the terms: 6 + x = 8.485281374 Solving 6 + x = 8.485281374 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + x = 8.485281374 + -6 Combine like terms: 6 + -6 = 0 0 + x = 8.485281374 + -6 x = 8.485281374 + -6 Combine like terms: 8.485281374 + -6 = 2.485281374 x = 2.485281374 Simplifying x = 2.485281374

Subproblem 2

x + 6 = -8.485281374 Simplifying x + 6 = -8.485281374 Reorder the terms: 6 + x = -8.485281374 Solving 6 + x = -8.485281374 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + x = -8.485281374 + -6 Combine like terms: 6 + -6 = 0 0 + x = -8.485281374 + -6 x = -8.485281374 + -6 Combine like terms: -8.485281374 + -6 = -14.485281374 x = -14.485281374 Simplifying x = -14.485281374

Solution

The solution to the problem is based on the solutions from the subproblems. x = {2.485281374, -14.485281374}

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