(r-2)(r+8)=-5

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Solution for (r-2)(r+8)=-5 equation:


Simplifying
(r + -2)(r + 8) = -5

Reorder the terms:
(-2 + r)(r + 8) = -5

Reorder the terms:
(-2 + r)(8 + r) = -5

Multiply (-2 + r) * (8 + r)
(-2(8 + r) + r(8 + r)) = -5
((8 * -2 + r * -2) + r(8 + r)) = -5
((-16 + -2r) + r(8 + r)) = -5
(-16 + -2r + (8 * r + r * r)) = -5
(-16 + -2r + (8r + r2)) = -5

Combine like terms: -2r + 8r = 6r
(-16 + 6r + r2) = -5

Solving
-16 + 6r + r2 = -5

Solving for variable 'r'.

Reorder the terms:
-16 + 5 + 6r + r2 = -5 + 5

Combine like terms: -16 + 5 = -11
-11 + 6r + r2 = -5 + 5

Combine like terms: -5 + 5 = 0
-11 + 6r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '11' to each side of the equation.
-11 + 6r + 11 + r2 = 0 + 11

Reorder the terms:
-11 + 11 + 6r + r2 = 0 + 11

Combine like terms: -11 + 11 = 0
0 + 6r + r2 = 0 + 11
6r + r2 = 0 + 11

Combine like terms: 0 + 11 = 11
6r + r2 = 11

The r term is 6r.  Take half its coefficient (3).
Square it (9) and add it to both sides.

Add '9' to each side of the equation.
6r + 9 + r2 = 11 + 9

Reorder the terms:
9 + 6r + r2 = 11 + 9

Combine like terms: 11 + 9 = 20
9 + 6r + r2 = 20

Factor a perfect square on the left side:
(r + 3)(r + 3) = 20

Calculate the square root of the right side: 4.472135955

Break this problem into two subproblems by setting 
(r + 3) equal to 4.472135955 and -4.472135955.

Subproblem 1

r + 3 = 4.472135955 Simplifying r + 3 = 4.472135955 Reorder the terms: 3 + r = 4.472135955 Solving 3 + r = 4.472135955 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-3' to each side of the equation. 3 + -3 + r = 4.472135955 + -3 Combine like terms: 3 + -3 = 0 0 + r = 4.472135955 + -3 r = 4.472135955 + -3 Combine like terms: 4.472135955 + -3 = 1.472135955 r = 1.472135955 Simplifying r = 1.472135955

Subproblem 2

r + 3 = -4.472135955 Simplifying r + 3 = -4.472135955 Reorder the terms: 3 + r = -4.472135955 Solving 3 + r = -4.472135955 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-3' to each side of the equation. 3 + -3 + r = -4.472135955 + -3 Combine like terms: 3 + -3 = 0 0 + r = -4.472135955 + -3 r = -4.472135955 + -3 Combine like terms: -4.472135955 + -3 = -7.472135955 r = -7.472135955 Simplifying r = -7.472135955

Solution

The solution to the problem is based on the solutions from the subproblems. r = {1.472135955, -7.472135955}

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