r^2-20r-36=4

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Solution for r^2-20r-36=4 equation:


Simplifying
r2 + -20r + -36 = 4

Reorder the terms:
-36 + -20r + r2 = 4

Solving
-36 + -20r + r2 = 4

Solving for variable 'r'.

Reorder the terms:
-36 + -4 + -20r + r2 = 4 + -4

Combine like terms: -36 + -4 = -40
-40 + -20r + r2 = 4 + -4

Combine like terms: 4 + -4 = 0
-40 + -20r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '40' to each side of the equation.
-40 + -20r + 40 + r2 = 0 + 40

Reorder the terms:
-40 + 40 + -20r + r2 = 0 + 40

Combine like terms: -40 + 40 = 0
0 + -20r + r2 = 0 + 40
-20r + r2 = 0 + 40

Combine like terms: 0 + 40 = 40
-20r + r2 = 40

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 = 40 + 100

Reorder the terms:
100 + -20r + r2 = 40 + 100

Combine like terms: 40 + 100 = 140
100 + -20r + r2 = 140

Factor a perfect square on the left side:
(r + -10)(r + -10) = 140

Calculate the square root of the right side: 11.832159566

Break this problem into two subproblems by setting 
(r + -10) equal to 11.832159566 and -11.832159566.

Subproblem 1

r + -10 = 11.832159566 Simplifying r + -10 = 11.832159566 Reorder the terms: -10 + r = 11.832159566 Solving -10 + r = 11.832159566 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 = 11.832159566 + 10 Combine like terms: -10 + 10 = 0 0 + r = 11.832159566 + 10 r = 11.832159566 + 10 Combine like terms: 11.832159566 + 10 = 21.832159566 r = 21.832159566 Simplifying r = 21.832159566

Subproblem 2

r + -10 = -11.832159566 Simplifying r + -10 = -11.832159566 Reorder the terms: -10 + r = -11.832159566 Solving -10 + r = -11.832159566 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 = -11.832159566 + 10 Combine like terms: -10 + 10 = 0 0 + r = -11.832159566 + 10 r = -11.832159566 + 10 Combine like terms: -11.832159566 + 10 = -1.832159566 r = -1.832159566 Simplifying r = -1.832159566

Solution

The solution to the problem is based on the solutions from the subproblems. r = {21.832159566, -1.832159566}

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