-6r+2r(r+2)-5=20

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Solution for -6r+2r(r+2)-5=20 equation:


Simplifying
-6r + 2r(r + 2) + -5 = 20

Reorder the terms:
-6r + 2r(2 + r) + -5 = 20
-6r + (2 * 2r + r * 2r) + -5 = 20
-6r + (4r + 2r2) + -5 = 20

Reorder the terms:
-5 + -6r + 4r + 2r2 = 20

Combine like terms: -6r + 4r = -2r
-5 + -2r + 2r2 = 20

Solving
-5 + -2r + 2r2 = 20

Solving for variable 'r'.

Reorder the terms:
-5 + -20 + -2r + 2r2 = 20 + -20

Combine like terms: -5 + -20 = -25
-25 + -2r + 2r2 = 20 + -20

Combine like terms: 20 + -20 = 0
-25 + -2r + 2r2 = 0

Begin completing the square.  Divide all terms by
2 the coefficient of the squared term: 

Divide each side by '2'.
-12.5 + -1r + r2 = 0

Move the constant term to the right:

Add '12.5' to each side of the equation.
-12.5 + -1r + 12.5 + r2 = 0 + 12.5

Reorder the terms:
-12.5 + 12.5 + -1r + r2 = 0 + 12.5

Combine like terms: -12.5 + 12.5 = 0.0
0.0 + -1r + r2 = 0 + 12.5
-1r + r2 = 0 + 12.5

Combine like terms: 0 + 12.5 = 12.5
-1r + r2 = 12.5

The r term is -1r.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1r + 0.25 + r2 = 12.5 + 0.25

Reorder the terms:
0.25 + -1r + r2 = 12.5 + 0.25

Combine like terms: 12.5 + 0.25 = 12.75
0.25 + -1r + r2 = 12.75

Factor a perfect square on the left side:
(r + -0.5)(r + -0.5) = 12.75

Calculate the square root of the right side: 3.570714214

Break this problem into two subproblems by setting 
(r + -0.5) equal to 3.570714214 and -3.570714214.

Subproblem 1

r + -0.5 = 3.570714214 Simplifying r + -0.5 = 3.570714214 Reorder the terms: -0.5 + r = 3.570714214 Solving -0.5 + r = 3.570714214 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = 3.570714214 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = 3.570714214 + 0.5 r = 3.570714214 + 0.5 Combine like terms: 3.570714214 + 0.5 = 4.070714214 r = 4.070714214 Simplifying r = 4.070714214

Subproblem 2

r + -0.5 = -3.570714214 Simplifying r + -0.5 = -3.570714214 Reorder the terms: -0.5 + r = -3.570714214 Solving -0.5 + r = -3.570714214 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = -3.570714214 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = -3.570714214 + 0.5 r = -3.570714214 + 0.5 Combine like terms: -3.570714214 + 0.5 = -3.070714214 r = -3.070714214 Simplifying r = -3.070714214

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4.070714214, -3.070714214}

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