r^2+20r-47=0

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Solution for r^2+20r-47=0 equation:


Simplifying
r2 + 20r + -47 = 0

Reorder the terms:
-47 + 20r + r2 = 0

Solving
-47 + 20r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '47' to each side of the equation.
-47 + 20r + 47 + r2 = 0 + 47

Reorder the terms:
-47 + 47 + 20r + r2 = 0 + 47

Combine like terms: -47 + 47 = 0
0 + 20r + r2 = 0 + 47
20r + r2 = 0 + 47

Combine like terms: 0 + 47 = 47
20r + r2 = 47

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 = 47 + 100

Reorder the terms:
100 + 20r + r2 = 47 + 100

Combine like terms: 47 + 100 = 147
100 + 20r + r2 = 147

Factor a perfect square on the left side:
(r + 10)(r + 10) = 147

Calculate the square root of the right side: 12.124355653

Break this problem into two subproblems by setting 
(r + 10) equal to 12.124355653 and -12.124355653.

Subproblem 1

r + 10 = 12.124355653 Simplifying r + 10 = 12.124355653 Reorder the terms: 10 + r = 12.124355653 Solving 10 + r = 12.124355653 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 = 12.124355653 + -10 Combine like terms: 10 + -10 = 0 0 + r = 12.124355653 + -10 r = 12.124355653 + -10 Combine like terms: 12.124355653 + -10 = 2.124355653 r = 2.124355653 Simplifying r = 2.124355653

Subproblem 2

r + 10 = -12.124355653 Simplifying r + 10 = -12.124355653 Reorder the terms: 10 + r = -12.124355653 Solving 10 + r = -12.124355653 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 = -12.124355653 + -10 Combine like terms: 10 + -10 = 0 0 + r = -12.124355653 + -10 r = -12.124355653 + -10 Combine like terms: -12.124355653 + -10 = -22.124355653 r = -22.124355653 Simplifying r = -22.124355653

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.124355653, -22.124355653}

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