x^2=12x+21

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


Simplifying
x2 = 12x + 21

Reorder the terms:
x2 = 21 + 12x

Solving
x2 = 21 + 12x

Solving for variable 'x'.

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

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

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

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

Begin completing the square.

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + -12x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + -12x + x2 = 0 + 21

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

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

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 = 21 + 36

Reorder the terms:
36 + -12x + x2 = 21 + 36

Combine like terms: 21 + 36 = 57
36 + -12x + x2 = 57

Factor a perfect square on the left side:
(x + -6)(x + -6) = 57

Calculate the square root of the right side: 7.549834435

Break this problem into two subproblems by setting 
(x + -6) equal to 7.549834435 and -7.549834435.

Subproblem 1

x + -6 = 7.549834435 Simplifying x + -6 = 7.549834435 Reorder the terms: -6 + x = 7.549834435 Solving -6 + x = 7.549834435 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 = 7.549834435 + 6 Combine like terms: -6 + 6 = 0 0 + x = 7.549834435 + 6 x = 7.549834435 + 6 Combine like terms: 7.549834435 + 6 = 13.549834435 x = 13.549834435 Simplifying x = 13.549834435

Subproblem 2

x + -6 = -7.549834435 Simplifying x + -6 = -7.549834435 Reorder the terms: -6 + x = -7.549834435 Solving -6 + x = -7.549834435 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 = -7.549834435 + 6 Combine like terms: -6 + 6 = 0 0 + x = -7.549834435 + 6 x = -7.549834435 + 6 Combine like terms: -7.549834435 + 6 = -1.549834435 x = -1.549834435 Simplifying x = -1.549834435

Solution

The solution to the problem is based on the solutions from the subproblems. x = {13.549834435, -1.549834435}

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