(r+5)(r+3)=18

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Solution for (r+5)(r+3)=18 equation:


Simplifying
(r + 5)(r + 3) = 18

Reorder the terms:
(5 + r)(r + 3) = 18

Reorder the terms:
(5 + r)(3 + r) = 18

Multiply (5 + r) * (3 + r)
(5(3 + r) + r(3 + r)) = 18
((3 * 5 + r * 5) + r(3 + r)) = 18
((15 + 5r) + r(3 + r)) = 18
(15 + 5r + (3 * r + r * r)) = 18
(15 + 5r + (3r + r2)) = 18

Combine like terms: 5r + 3r = 8r
(15 + 8r + r2) = 18

Solving
15 + 8r + r2 = 18

Solving for variable 'r'.

Reorder the terms:
15 + -18 + 8r + r2 = 18 + -18

Combine like terms: 15 + -18 = -3
-3 + 8r + r2 = 18 + -18

Combine like terms: 18 + -18 = 0
-3 + 8r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '3' to each side of the equation.
-3 + 8r + 3 + r2 = 0 + 3

Reorder the terms:
-3 + 3 + 8r + r2 = 0 + 3

Combine like terms: -3 + 3 = 0
0 + 8r + r2 = 0 + 3
8r + r2 = 0 + 3

Combine like terms: 0 + 3 = 3
8r + r2 = 3

The r term is 8r.  Take half its coefficient (4).
Square it (16) and add it to both sides.

Add '16' to each side of the equation.
8r + 16 + r2 = 3 + 16

Reorder the terms:
16 + 8r + r2 = 3 + 16

Combine like terms: 3 + 16 = 19
16 + 8r + r2 = 19

Factor a perfect square on the left side:
(r + 4)(r + 4) = 19

Calculate the square root of the right side: 4.358898944

Break this problem into two subproblems by setting 
(r + 4) equal to 4.358898944 and -4.358898944.

Subproblem 1

r + 4 = 4.358898944 Simplifying r + 4 = 4.358898944 Reorder the terms: 4 + r = 4.358898944 Solving 4 + r = 4.358898944 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + r = 4.358898944 + -4 Combine like terms: 4 + -4 = 0 0 + r = 4.358898944 + -4 r = 4.358898944 + -4 Combine like terms: 4.358898944 + -4 = 0.358898944 r = 0.358898944 Simplifying r = 0.358898944

Subproblem 2

r + 4 = -4.358898944 Simplifying r + 4 = -4.358898944 Reorder the terms: 4 + r = -4.358898944 Solving 4 + r = -4.358898944 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-4' to each side of the equation. 4 + -4 + r = -4.358898944 + -4 Combine like terms: 4 + -4 = 0 0 + r = -4.358898944 + -4 r = -4.358898944 + -4 Combine like terms: -4.358898944 + -4 = -8.358898944 r = -8.358898944 Simplifying r = -8.358898944

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.358898944, -8.358898944}

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