x^2-13x=-21

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Solution for x^2-13x=-21 equation:


Simplifying
x2 + -13x = -21

Reorder the terms:
-13x + x2 = -21

Solving
-13x + x2 = -21

Solving for variable 'x'.

Reorder the terms:
21 + -13x + x2 = -21 + 21

Combine like terms: -21 + 21 = 0
21 + -13x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-21' to each side of the equation.
21 + -13x + -21 + x2 = 0 + -21

Reorder the terms:
21 + -21 + -13x + x2 = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -13x + x2 = 0 + -21
-13x + x2 = 0 + -21

Combine like terms: 0 + -21 = -21
-13x + x2 = -21

The x term is -13x.  Take half its coefficient (-6.5).
Square it (42.25) and add it to both sides.

Add '42.25' to each side of the equation.
-13x + 42.25 + x2 = -21 + 42.25

Reorder the terms:
42.25 + -13x + x2 = -21 + 42.25

Combine like terms: -21 + 42.25 = 21.25
42.25 + -13x + x2 = 21.25

Factor a perfect square on the left side:
(x + -6.5)(x + -6.5) = 21.25

Calculate the square root of the right side: 4.609772229

Break this problem into two subproblems by setting 
(x + -6.5) equal to 4.609772229 and -4.609772229.

Subproblem 1

x + -6.5 = 4.609772229 Simplifying x + -6.5 = 4.609772229 Reorder the terms: -6.5 + x = 4.609772229 Solving -6.5 + x = 4.609772229 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '6.5' to each side of the equation. -6.5 + 6.5 + x = 4.609772229 + 6.5 Combine like terms: -6.5 + 6.5 = 0.0 0.0 + x = 4.609772229 + 6.5 x = 4.609772229 + 6.5 Combine like terms: 4.609772229 + 6.5 = 11.109772229 x = 11.109772229 Simplifying x = 11.109772229

Subproblem 2

x + -6.5 = -4.609772229 Simplifying x + -6.5 = -4.609772229 Reorder the terms: -6.5 + x = -4.609772229 Solving -6.5 + x = -4.609772229 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '6.5' to each side of the equation. -6.5 + 6.5 + x = -4.609772229 + 6.5 Combine like terms: -6.5 + 6.5 = 0.0 0.0 + x = -4.609772229 + 6.5 x = -4.609772229 + 6.5 Combine like terms: -4.609772229 + 6.5 = 1.890227771 x = 1.890227771 Simplifying x = 1.890227771

Solution

The solution to the problem is based on the solutions from the subproblems. x = {11.109772229, 1.890227771}

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