r^2-8r=-8

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Solution for r^2-8r=-8 equation:


Simplifying
r2 + -8r = -8

Reorder the terms:
-8r + r2 = -8

Solving
-8r + r2 = -8

Solving for variable 'r'.

Reorder the terms:
8 + -8r + r2 = -8 + 8

Combine like terms: -8 + 8 = 0
8 + -8r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '-8' to each side of the equation.
8 + -8r + -8 + r2 = 0 + -8

Reorder the terms:
8 + -8 + -8r + r2 = 0 + -8

Combine like terms: 8 + -8 = 0
0 + -8r + r2 = 0 + -8
-8r + r2 = 0 + -8

Combine like terms: 0 + -8 = -8
-8r + r2 = -8

The r term is -8r.  Take half its coefficient (-4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
-8r + 16 + r2 = -8 + 16

Reorder the terms:
16 + -8r + r2 = -8 + 16

Combine like terms: -8 + 16 = 8
16 + -8r + r2 = 8

Factor a perfect square on the left side:
(r + -4)(r + -4) = 8

Calculate the square root of the right side: 2.828427125

Break this problem into two subproblems by setting 
(r + -4) equal to 2.828427125 and -2.828427125.

Subproblem 1

r + -4 = 2.828427125 Simplifying r + -4 = 2.828427125 Reorder the terms: -4 + r = 2.828427125 Solving -4 + r = 2.828427125 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + r = 2.828427125 + 4 Combine like terms: -4 + 4 = 0 0 + r = 2.828427125 + 4 r = 2.828427125 + 4 Combine like terms: 2.828427125 + 4 = 6.828427125 r = 6.828427125 Simplifying r = 6.828427125

Subproblem 2

r + -4 = -2.828427125 Simplifying r + -4 = -2.828427125 Reorder the terms: -4 + r = -2.828427125 Solving -4 + r = -2.828427125 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '4' to each side of the equation. -4 + 4 + r = -2.828427125 + 4 Combine like terms: -4 + 4 = 0 0 + r = -2.828427125 + 4 r = -2.828427125 + 4 Combine like terms: -2.828427125 + 4 = 1.171572875 r = 1.171572875 Simplifying r = 1.171572875

Solution

The solution to the problem is based on the solutions from the subproblems. r = {6.828427125, 1.171572875}

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