0=x^2-12x+21

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Solution for 0=x^2-12x+21 equation:


Simplifying
0 = x2 + -12x + 21

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

Solving
0 = 21 + -12x + x2

Solving for variable 'x'.

Combine like terms: 0 + -21 = -21
-21 + 12x + -1x2 = 21 + -12x + x2 + -21 + 12x + -1x2

Reorder the terms:
-21 + 12x + -1x2 = 21 + -21 + -12x + 12x + x2 + -1x2

Combine like terms: 21 + -21 = 0
-21 + 12x + -1x2 = 0 + -12x + 12x + x2 + -1x2
-21 + 12x + -1x2 = -12x + 12x + x2 + -1x2

Combine like terms: -12x + 12x = 0
-21 + 12x + -1x2 = 0 + x2 + -1x2
-21 + 12x + -1x2 = x2 + -1x2

Combine like terms: x2 + -1x2 = 0
-21 + 12x + -1x2 = 0

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

Divide each side by '-1'.
21 + -12x + x2 = 0

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 = 15
36 + -12x + x2 = 15

Factor a perfect square on the left side:
(x + -6)(x + -6) = 15

Calculate the square root of the right side: 3.872983346

Break this problem into two subproblems by setting 
(x + -6) equal to 3.872983346 and -3.872983346.

Subproblem 1

x + -6 = 3.872983346 Simplifying x + -6 = 3.872983346 Reorder the terms: -6 + x = 3.872983346 Solving -6 + x = 3.872983346 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 = 3.872983346 + 6 Combine like terms: -6 + 6 = 0 0 + x = 3.872983346 + 6 x = 3.872983346 + 6 Combine like terms: 3.872983346 + 6 = 9.872983346 x = 9.872983346 Simplifying x = 9.872983346

Subproblem 2

x + -6 = -3.872983346 Simplifying x + -6 = -3.872983346 Reorder the terms: -6 + x = -3.872983346 Solving -6 + x = -3.872983346 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 = -3.872983346 + 6 Combine like terms: -6 + 6 = 0 0 + x = -3.872983346 + 6 x = -3.872983346 + 6 Combine like terms: -3.872983346 + 6 = 2.127016654 x = 2.127016654 Simplifying x = 2.127016654

Solution

The solution to the problem is based on the solutions from the subproblems. x = {9.872983346, 2.127016654}

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