x^2-21=6x

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Solution for x^2-21=6x equation:


Simplifying
x2 + -21 = 6x

Reorder the terms:
-21 + x2 = 6x

Solving
-21 + x2 = 6x

Solving for variable 'x'.

Reorder the terms:
-21 + -6x + x2 = 6x + -6x

Combine like terms: 6x + -6x = 0
-21 + -6x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + -6x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + -6x + x2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -6x + x2 = 0 + 21
-6x + x2 = 0 + 21

Combine like terms: 0 + 21 = 21
-6x + x2 = 21

The x term is -6x.  Take half its coefficient (-3).
Square it (9) and add it to both sides.

Add '9' to each side of the equation.
-6x + 9 + x2 = 21 + 9

Reorder the terms:
9 + -6x + x2 = 21 + 9

Combine like terms: 21 + 9 = 30
9 + -6x + x2 = 30

Factor a perfect square on the left side:
(x + -3)(x + -3) = 30

Calculate the square root of the right side: 5.477225575

Break this problem into two subproblems by setting 
(x + -3) equal to 5.477225575 and -5.477225575.

Subproblem 1

x + -3 = 5.477225575 Simplifying x + -3 = 5.477225575 Reorder the terms: -3 + x = 5.477225575 Solving -3 + x = 5.477225575 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3' to each side of the equation. -3 + 3 + x = 5.477225575 + 3 Combine like terms: -3 + 3 = 0 0 + x = 5.477225575 + 3 x = 5.477225575 + 3 Combine like terms: 5.477225575 + 3 = 8.477225575 x = 8.477225575 Simplifying x = 8.477225575

Subproblem 2

x + -3 = -5.477225575 Simplifying x + -3 = -5.477225575 Reorder the terms: -3 + x = -5.477225575 Solving -3 + x = -5.477225575 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '3' to each side of the equation. -3 + 3 + x = -5.477225575 + 3 Combine like terms: -3 + 3 = 0 0 + x = -5.477225575 + 3 x = -5.477225575 + 3 Combine like terms: -5.477225575 + 3 = -2.477225575 x = -2.477225575 Simplifying x = -2.477225575

Solution

The solution to the problem is based on the solutions from the subproblems. x = {8.477225575, -2.477225575}

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