x^2-21x=-21

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


Simplifying
x2 + -21x = -21

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

Solving
-21x + x2 = -21

Solving for variable 'x'.

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

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

Begin completing the square.

Move the constant term to the right:

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

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

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

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

The x term is -21x.  Take half its coefficient (-10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
-21x + 110.25 + x2 = -21 + 110.25

Reorder the terms:
110.25 + -21x + x2 = -21 + 110.25

Combine like terms: -21 + 110.25 = 89.25
110.25 + -21x + x2 = 89.25

Factor a perfect square on the left side:
(x + -10.5)(x + -10.5) = 89.25

Calculate the square root of the right side: 9.447221814

Break this problem into two subproblems by setting 
(x + -10.5) equal to 9.447221814 and -9.447221814.

Subproblem 1

x + -10.5 = 9.447221814 Simplifying x + -10.5 = 9.447221814 Reorder the terms: -10.5 + x = 9.447221814 Solving -10.5 + x = 9.447221814 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = 9.447221814 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = 9.447221814 + 10.5 x = 9.447221814 + 10.5 Combine like terms: 9.447221814 + 10.5 = 19.947221814 x = 19.947221814 Simplifying x = 19.947221814

Subproblem 2

x + -10.5 = -9.447221814 Simplifying x + -10.5 = -9.447221814 Reorder the terms: -10.5 + x = -9.447221814 Solving -10.5 + x = -9.447221814 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '10.5' to each side of the equation. -10.5 + 10.5 + x = -9.447221814 + 10.5 Combine like terms: -10.5 + 10.5 = 0.0 0.0 + x = -9.447221814 + 10.5 x = -9.447221814 + 10.5 Combine like terms: -9.447221814 + 10.5 = 1.052778186 x = 1.052778186 Simplifying x = 1.052778186

Solution

The solution to the problem is based on the solutions from the subproblems. x = {19.947221814, 1.052778186}

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