r^2+20r-80=-5

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Solution for r^2+20r-80=-5 equation:


Simplifying
r2 + 20r + -80 = -5

Reorder the terms:
-80 + 20r + r2 = -5

Solving
-80 + 20r + r2 = -5

Solving for variable 'r'.

Reorder the terms:
-80 + 5 + 20r + r2 = -5 + 5

Combine like terms: -80 + 5 = -75
-75 + 20r + r2 = -5 + 5

Combine like terms: -5 + 5 = 0
-75 + 20r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '75' to each side of the equation.
-75 + 20r + 75 + r2 = 0 + 75

Reorder the terms:
-75 + 75 + 20r + r2 = 0 + 75

Combine like terms: -75 + 75 = 0
0 + 20r + r2 = 0 + 75
20r + r2 = 0 + 75

Combine like terms: 0 + 75 = 75
20r + r2 = 75

The r term is 20r.  Take half its coefficient (10).
Square it (100) and add it to both sides.

Add '100' to each side of the equation.
20r + 100 + r2 = 75 + 100

Reorder the terms:
100 + 20r + r2 = 75 + 100

Combine like terms: 75 + 100 = 175
100 + 20r + r2 = 175

Factor a perfect square on the left side:
(r + 10)(r + 10) = 175

Calculate the square root of the right side: 13.228756555

Break this problem into two subproblems by setting 
(r + 10) equal to 13.228756555 and -13.228756555.

Subproblem 1

r + 10 = 13.228756555 Simplifying r + 10 = 13.228756555 Reorder the terms: 10 + r = 13.228756555 Solving 10 + r = 13.228756555 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-10' to each side of the equation. 10 + -10 + r = 13.228756555 + -10 Combine like terms: 10 + -10 = 0 0 + r = 13.228756555 + -10 r = 13.228756555 + -10 Combine like terms: 13.228756555 + -10 = 3.228756555 r = 3.228756555 Simplifying r = 3.228756555

Subproblem 2

r + 10 = -13.228756555 Simplifying r + 10 = -13.228756555 Reorder the terms: 10 + r = -13.228756555 Solving 10 + r = -13.228756555 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-10' to each side of the equation. 10 + -10 + r = -13.228756555 + -10 Combine like terms: 10 + -10 = 0 0 + r = -13.228756555 + -10 r = -13.228756555 + -10 Combine like terms: -13.228756555 + -10 = -23.228756555 r = -23.228756555 Simplifying r = -23.228756555

Solution

The solution to the problem is based on the solutions from the subproblems. r = {3.228756555, -23.228756555}

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