3x^2-21x=2x^2-5x-12

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Solution for 3x^2-21x=2x^2-5x-12 equation:


Simplifying
3x2 + -21x = 2x2 + -5x + -12

Reorder the terms:
-21x + 3x2 = 2x2 + -5x + -12

Reorder the terms:
-21x + 3x2 = -12 + -5x + 2x2

Solving
-21x + 3x2 = -12 + -5x + 2x2

Solving for variable 'x'.

Reorder the terms:
12 + -21x + 5x + 3x2 + -2x2 = -12 + -5x + 2x2 + 12 + 5x + -2x2

Combine like terms: -21x + 5x = -16x
12 + -16x + 3x2 + -2x2 = -12 + -5x + 2x2 + 12 + 5x + -2x2

Combine like terms: 3x2 + -2x2 = 1x2
12 + -16x + 1x2 = -12 + -5x + 2x2 + 12 + 5x + -2x2

Reorder the terms:
12 + -16x + 1x2 = -12 + 12 + -5x + 5x + 2x2 + -2x2

Combine like terms: -12 + 12 = 0
12 + -16x + 1x2 = 0 + -5x + 5x + 2x2 + -2x2
12 + -16x + 1x2 = -5x + 5x + 2x2 + -2x2

Combine like terms: -5x + 5x = 0
12 + -16x + 1x2 = 0 + 2x2 + -2x2
12 + -16x + 1x2 = 2x2 + -2x2

Combine like terms: 2x2 + -2x2 = 0
12 + -16x + 1x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-12' to each side of the equation.
12 + -16x + -12 + x2 = 0 + -12

Reorder the terms:
12 + -12 + -16x + x2 = 0 + -12

Combine like terms: 12 + -12 = 0
0 + -16x + x2 = 0 + -12
-16x + x2 = 0 + -12

Combine like terms: 0 + -12 = -12
-16x + x2 = -12

The x term is -16x.  Take half its coefficient (-8).
Square it (64) and add it to both sides.

Add '64' to each side of the equation.
-16x + 64 + x2 = -12 + 64

Reorder the terms:
64 + -16x + x2 = -12 + 64

Combine like terms: -12 + 64 = 52
64 + -16x + x2 = 52

Factor a perfect square on the left side:
(x + -8)(x + -8) = 52

Calculate the square root of the right side: 7.211102551

Break this problem into two subproblems by setting 
(x + -8) equal to 7.211102551 and -7.211102551.

Subproblem 1

x + -8 = 7.211102551 Simplifying x + -8 = 7.211102551 Reorder the terms: -8 + x = 7.211102551 Solving -8 + x = 7.211102551 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '8' to each side of the equation. -8 + 8 + x = 7.211102551 + 8 Combine like terms: -8 + 8 = 0 0 + x = 7.211102551 + 8 x = 7.211102551 + 8 Combine like terms: 7.211102551 + 8 = 15.211102551 x = 15.211102551 Simplifying x = 15.211102551

Subproblem 2

x + -8 = -7.211102551 Simplifying x + -8 = -7.211102551 Reorder the terms: -8 + x = -7.211102551 Solving -8 + x = -7.211102551 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '8' to each side of the equation. -8 + 8 + x = -7.211102551 + 8 Combine like terms: -8 + 8 = 0 0 + x = -7.211102551 + 8 x = -7.211102551 + 8 Combine like terms: -7.211102551 + 8 = 0.788897449 x = 0.788897449 Simplifying x = 0.788897449

Solution

The solution to the problem is based on the solutions from the subproblems. x = {15.211102551, 0.788897449}

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