(r-4)(r+16)=-55

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Solution for (r-4)(r+16)=-55 equation:


Simplifying
(r + -4)(r + 16) = -55

Reorder the terms:
(-4 + r)(r + 16) = -55

Reorder the terms:
(-4 + r)(16 + r) = -55

Multiply (-4 + r) * (16 + r)
(-4(16 + r) + r(16 + r)) = -55
((16 * -4 + r * -4) + r(16 + r)) = -55
((-64 + -4r) + r(16 + r)) = -55
(-64 + -4r + (16 * r + r * r)) = -55
(-64 + -4r + (16r + r2)) = -55

Combine like terms: -4r + 16r = 12r
(-64 + 12r + r2) = -55

Solving
-64 + 12r + r2 = -55

Solving for variable 'r'.

Reorder the terms:
-64 + 55 + 12r + r2 = -55 + 55

Combine like terms: -64 + 55 = -9
-9 + 12r + r2 = -55 + 55

Combine like terms: -55 + 55 = 0
-9 + 12r + r2 = 0

Begin completing the square.

Move the constant term to the right:

Add '9' to each side of the equation.
-9 + 12r + 9 + r2 = 0 + 9

Reorder the terms:
-9 + 9 + 12r + r2 = 0 + 9

Combine like terms: -9 + 9 = 0
0 + 12r + r2 = 0 + 9
12r + r2 = 0 + 9

Combine like terms: 0 + 9 = 9
12r + r2 = 9

The r term is 12r.  Take half its coefficient (6).
Square it (36) and add it to both sides.

Add '36' to each side of the equation.
12r + 36 + r2 = 9 + 36

Reorder the terms:
36 + 12r + r2 = 9 + 36

Combine like terms: 9 + 36 = 45
36 + 12r + r2 = 45

Factor a perfect square on the left side:
(r + 6)(r + 6) = 45

Calculate the square root of the right side: 6.708203933

Break this problem into two subproblems by setting 
(r + 6) equal to 6.708203933 and -6.708203933.

Subproblem 1

r + 6 = 6.708203933 Simplifying r + 6 = 6.708203933 Reorder the terms: 6 + r = 6.708203933 Solving 6 + r = 6.708203933 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + r = 6.708203933 + -6 Combine like terms: 6 + -6 = 0 0 + r = 6.708203933 + -6 r = 6.708203933 + -6 Combine like terms: 6.708203933 + -6 = 0.708203933 r = 0.708203933 Simplifying r = 0.708203933

Subproblem 2

r + 6 = -6.708203933 Simplifying r + 6 = -6.708203933 Reorder the terms: 6 + r = -6.708203933 Solving 6 + r = -6.708203933 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-6' to each side of the equation. 6 + -6 + r = -6.708203933 + -6 Combine like terms: 6 + -6 = 0 0 + r = -6.708203933 + -6 r = -6.708203933 + -6 Combine like terms: -6.708203933 + -6 = -12.708203933 r = -12.708203933 Simplifying r = -12.708203933

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.708203933, -12.708203933}

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