r^2-r-r-20=0

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


Simplifying
r2 + -1r + -1r + -20 = 0

Reorder the terms:
-20 + -1r + -1r + r2 = 0

Combine like terms: -1r + -1r = -2r
-20 + -2r + r2 = 0

Solving
-20 + -2r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '20' to each side of the equation.
-20 + -2r + 20 + r2 = 0 + 20

Reorder the terms:
-20 + 20 + -2r + r2 = 0 + 20

Combine like terms: -20 + 20 = 0
0 + -2r + r2 = 0 + 20
-2r + r2 = 0 + 20

Combine like terms: 0 + 20 = 20
-2r + r2 = 20

The r term is -2r.  Take half its coefficient (-1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
-2r + 1 + r2 = 20 + 1

Reorder the terms:
1 + -2r + r2 = 20 + 1

Combine like terms: 20 + 1 = 21
1 + -2r + r2 = 21

Factor a perfect square on the left side:
(r + -1)(r + -1) = 21

Calculate the square root of the right side: 4.582575695

Break this problem into two subproblems by setting 
(r + -1) equal to 4.582575695 and -4.582575695.

Subproblem 1

r + -1 = 4.582575695 Simplifying r + -1 = 4.582575695 Reorder the terms: -1 + r = 4.582575695 Solving -1 + r = 4.582575695 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + r = 4.582575695 + 1 Combine like terms: -1 + 1 = 0 0 + r = 4.582575695 + 1 r = 4.582575695 + 1 Combine like terms: 4.582575695 + 1 = 5.582575695 r = 5.582575695 Simplifying r = 5.582575695

Subproblem 2

r + -1 = -4.582575695 Simplifying r + -1 = -4.582575695 Reorder the terms: -1 + r = -4.582575695 Solving -1 + r = -4.582575695 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '1' to each side of the equation. -1 + 1 + r = -4.582575695 + 1 Combine like terms: -1 + 1 = 0 0 + r = -4.582575695 + 1 r = -4.582575695 + 1 Combine like terms: -4.582575695 + 1 = -3.582575695 r = -3.582575695 Simplifying r = -3.582575695

Solution

The solution to the problem is based on the solutions from the subproblems. r = {5.582575695, -3.582575695}

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