r^2+20r-4=0

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Solution for r^2+20r-4=0 equation:


Simplifying
r2 + 20r + -4 = 0

Reorder the terms:
-4 + 20r + r2 = 0

Solving
-4 + 20r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '4' to each side of the equation.
-4 + 20r + 4 + r2 = 0 + 4

Reorder the terms:
-4 + 4 + 20r + r2 = 0 + 4

Combine like terms: -4 + 4 = 0
0 + 20r + r2 = 0 + 4
20r + r2 = 0 + 4

Combine like terms: 0 + 4 = 4
20r + r2 = 4

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 = 4 + 100

Reorder the terms:
100 + 20r + r2 = 4 + 100

Combine like terms: 4 + 100 = 104
100 + 20r + r2 = 104

Factor a perfect square on the left side:
(r + 10)(r + 10) = 104

Calculate the square root of the right side: 10.198039027

Break this problem into two subproblems by setting 
(r + 10) equal to 10.198039027 and -10.198039027.

Subproblem 1

r + 10 = 10.198039027 Simplifying r + 10 = 10.198039027 Reorder the terms: 10 + r = 10.198039027 Solving 10 + r = 10.198039027 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 = 10.198039027 + -10 Combine like terms: 10 + -10 = 0 0 + r = 10.198039027 + -10 r = 10.198039027 + -10 Combine like terms: 10.198039027 + -10 = 0.198039027 r = 0.198039027 Simplifying r = 0.198039027

Subproblem 2

r + 10 = -10.198039027 Simplifying r + 10 = -10.198039027 Reorder the terms: 10 + r = -10.198039027 Solving 10 + r = -10.198039027 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 = -10.198039027 + -10 Combine like terms: 10 + -10 = 0 0 + r = -10.198039027 + -10 r = -10.198039027 + -10 Combine like terms: -10.198039027 + -10 = -20.198039027 r = -20.198039027 Simplifying r = -20.198039027

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.198039027, -20.198039027}

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