(r-4)(r+8)=-9

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Solution for (r-4)(r+8)=-9 equation:


Simplifying
(r + -4)(r + 8) = -9

Reorder the terms:
(-4 + r)(r + 8) = -9

Reorder the terms:
(-4 + r)(8 + r) = -9

Multiply (-4 + r) * (8 + r)
(-4(8 + r) + r(8 + r)) = -9
((8 * -4 + r * -4) + r(8 + r)) = -9
((-32 + -4r) + r(8 + r)) = -9
(-32 + -4r + (8 * r + r * r)) = -9
(-32 + -4r + (8r + r2)) = -9

Combine like terms: -4r + 8r = 4r
(-32 + 4r + r2) = -9

Solving
-32 + 4r + r2 = -9

Solving for variable 'r'.

Reorder the terms:
-32 + 9 + 4r + r2 = -9 + 9

Combine like terms: -32 + 9 = -23
-23 + 4r + r2 = -9 + 9

Combine like terms: -9 + 9 = 0
-23 + 4r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '23' to each side of the equation.
-23 + 4r + 23 + r2 = 0 + 23

Reorder the terms:
-23 + 23 + 4r + r2 = 0 + 23

Combine like terms: -23 + 23 = 0
0 + 4r + r2 = 0 + 23
4r + r2 = 0 + 23

Combine like terms: 0 + 23 = 23
4r + r2 = 23

The r term is 4r.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4r + 4 + r2 = 23 + 4

Reorder the terms:
4 + 4r + r2 = 23 + 4

Combine like terms: 23 + 4 = 27
4 + 4r + r2 = 27

Factor a perfect square on the left side:
(r + 2)(r + 2) = 27

Calculate the square root of the right side: 5.196152423

Break this problem into two subproblems by setting 
(r + 2) equal to 5.196152423 and -5.196152423.

Subproblem 1

r + 2 = 5.196152423 Simplifying r + 2 = 5.196152423 Reorder the terms: 2 + r = 5.196152423 Solving 2 + r = 5.196152423 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + r = 5.196152423 + -2 Combine like terms: 2 + -2 = 0 0 + r = 5.196152423 + -2 r = 5.196152423 + -2 Combine like terms: 5.196152423 + -2 = 3.196152423 r = 3.196152423 Simplifying r = 3.196152423

Subproblem 2

r + 2 = -5.196152423 Simplifying r + 2 = -5.196152423 Reorder the terms: 2 + r = -5.196152423 Solving 2 + r = -5.196152423 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + r = -5.196152423 + -2 Combine like terms: 2 + -2 = 0 0 + r = -5.196152423 + -2 r = -5.196152423 + -2 Combine like terms: -5.196152423 + -2 = -7.196152423 r = -7.196152423 Simplifying r = -7.196152423

Solution

The solution to the problem is based on the solutions from the subproblems. r = {3.196152423, -7.196152423}

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