21=x^2-12x-2

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


Simplifying
21 = x2 + -12x + -2

Reorder the terms:
21 = -2 + -12x + x2

Solving
21 = -2 + -12x + x2

Solving for variable 'x'.

Combine like terms: 21 + 2 = 23
23 + 12x + -1x2 = -2 + -12x + x2 + 2 + 12x + -1x2

Reorder the terms:
23 + 12x + -1x2 = -2 + 2 + -12x + 12x + x2 + -1x2

Combine like terms: -2 + 2 = 0
23 + 12x + -1x2 = 0 + -12x + 12x + x2 + -1x2
23 + 12x + -1x2 = -12x + 12x + x2 + -1x2

Combine like terms: -12x + 12x = 0
23 + 12x + -1x2 = 0 + x2 + -1x2
23 + 12x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
23 + 12x + -1x2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
-23 + -12x + x2 = 0

Move the constant term to the right:

Add '23' to each side of the equation.
-23 + -12x + 23 + x2 = 0 + 23

Reorder the terms:
-23 + 23 + -12x + x2 = 0 + 23

Combine like terms: -23 + 23 = 0
0 + -12x + x2 = 0 + 23
-12x + x2 = 0 + 23

Combine like terms: 0 + 23 = 23
-12x + x2 = 23

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 = 23 + 36

Reorder the terms:
36 + -12x + x2 = 23 + 36

Combine like terms: 23 + 36 = 59
36 + -12x + x2 = 59

Factor a perfect square on the left side:
(x + -6)(x + -6) = 59

Calculate the square root of the right side: 7.681145748

Break this problem into two subproblems by setting 
(x + -6) equal to 7.681145748 and -7.681145748.

Subproblem 1

x + -6 = 7.681145748 Simplifying x + -6 = 7.681145748 Reorder the terms: -6 + x = 7.681145748 Solving -6 + x = 7.681145748 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 = 7.681145748 + 6 Combine like terms: -6 + 6 = 0 0 + x = 7.681145748 + 6 x = 7.681145748 + 6 Combine like terms: 7.681145748 + 6 = 13.681145748 x = 13.681145748 Simplifying x = 13.681145748

Subproblem 2

x + -6 = -7.681145748 Simplifying x + -6 = -7.681145748 Reorder the terms: -6 + x = -7.681145748 Solving -6 + x = -7.681145748 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 = -7.681145748 + 6 Combine like terms: -6 + 6 = 0 0 + x = -7.681145748 + 6 x = -7.681145748 + 6 Combine like terms: -7.681145748 + 6 = -1.681145748 x = -1.681145748 Simplifying x = -1.681145748

Solution

The solution to the problem is based on the solutions from the subproblems. x = {13.681145748, -1.681145748}

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