-2r^2+8r=-5

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Solution for -2r^2+8r=-5 equation:


Simplifying
-2r2 + 8r = -5

Reorder the terms:
8r + -2r2 = -5

Solving
8r + -2r2 = -5

Solving for variable 'r'.

Reorder the terms:
5 + 8r + -2r2 = -5 + 5

Combine like terms: -5 + 5 = 0
5 + 8r + -2r2 = 0

Begin completing the square.  Divide all terms by
-2 the coefficient of the squared term: 

Divide each side by '-2'.
-2.5 + -4r + r2 = 0

Move the constant term to the right:

Add '2.5' to each side of the equation.
-2.5 + -4r + 2.5 + r2 = 0 + 2.5

Reorder the terms:
-2.5 + 2.5 + -4r + r2 = 0 + 2.5

Combine like terms: -2.5 + 2.5 = 0.0
0.0 + -4r + r2 = 0 + 2.5
-4r + r2 = 0 + 2.5

Combine like terms: 0 + 2.5 = 2.5
-4r + r2 = 2.5

The r term is -4r.  Take half its coefficient (-2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
-4r + 4 + r2 = 2.5 + 4

Reorder the terms:
4 + -4r + r2 = 2.5 + 4

Combine like terms: 2.5 + 4 = 6.5
4 + -4r + r2 = 6.5

Factor a perfect square on the left side:
(r + -2)(r + -2) = 6.5

Calculate the square root of the right side: 2.549509757

Break this problem into two subproblems by setting 
(r + -2) equal to 2.549509757 and -2.549509757.

Subproblem 1

r + -2 = 2.549509757 Simplifying r + -2 = 2.549509757 Reorder the terms: -2 + r = 2.549509757 Solving -2 + r = 2.549509757 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + r = 2.549509757 + 2 Combine like terms: -2 + 2 = 0 0 + r = 2.549509757 + 2 r = 2.549509757 + 2 Combine like terms: 2.549509757 + 2 = 4.549509757 r = 4.549509757 Simplifying r = 4.549509757

Subproblem 2

r + -2 = -2.549509757 Simplifying r + -2 = -2.549509757 Reorder the terms: -2 + r = -2.549509757 Solving -2 + r = -2.549509757 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + r = -2.549509757 + 2 Combine like terms: -2 + 2 = 0 0 + r = -2.549509757 + 2 r = -2.549509757 + 2 Combine like terms: -2.549509757 + 2 = -0.549509757 r = -0.549509757 Simplifying r = -0.549509757

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4.549509757, -0.549509757}

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