168=2(x+9)(x-4)

Solution for 168=2(x+9)(x-4) equation:

Simplifying
168 = 2(x + 9)(x + -4)

Reorder the terms:
168 = 2(9 + x)(x + -4)

Reorder the terms:
168 = 2(9 + x)(-4 + x)

Multiply (9 + x) * (-4 + x)
168 = 2(9(-4 + x) + x(-4 + x))
168 = 2((-4 * 9 + x * 9) + x(-4 + x))
168 = 2((-36 + 9x) + x(-4 + x))
168 = 2(-36 + 9x + (-4 * x + x * x))
168 = 2(-36 + 9x + (-4x + x2))

Combine like terms: 9x + -4x = 5x
168 = 2(-36 + 5x + x2)
168 = (-36 * 2 + 5x * 2 + x2 * 2)
168 = (-72 + 10x + 2x2)

Solving
168 = -72 + 10x + 2x2

Solving for variable 'x'.

Combine like terms: 168 + 72 = 240
240 + -10x + -2x2 = -72 + 10x + 2x2 + 72 + -10x + -2x2

Reorder the terms:
240 + -10x + -2x2 = -72 + 72 + 10x + -10x + 2x2 + -2x2

Combine like terms: -72 + 72 = 0
240 + -10x + -2x2 = 0 + 10x + -10x + 2x2 + -2x2
240 + -10x + -2x2 = 10x + -10x + 2x2 + -2x2

Combine like terms: 10x + -10x = 0
240 + -10x + -2x2 = 0 + 2x2 + -2x2
240 + -10x + -2x2 = 2x2 + -2x2

Combine like terms: 2x2 + -2x2 = 0
240 + -10x + -2x2 = 0

Factor out the Greatest Common Factor (GCF), '2'.
2(120 + -5x + -1x2) = 0

Ignore the factor 2.
Subproblem 1
Set the factor '(120 + -5x + -1x2)' equal to zero and attempt to solve:

Simplifying
120 + -5x + -1x2 = 0

Solving
120 + -5x + -1x2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
-120 + 5x + x2 = 0

Move the constant term to the right:

Add '120' to each side of the equation.
-120 + 5x + 120 + x2 = 0 + 120

Reorder the terms:
-120 + 120 + 5x + x2 = 0 + 120

Combine like terms: -120 + 120 = 0
0 + 5x + x2 = 0 + 120
5x + x2 = 0 + 120

Combine like terms: 0 + 120 = 120
5x + x2 = 120

The x term is 5x.  Take half its coefficient (2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
5x + 6.25 + x2 = 120 + 6.25

Reorder the terms:
6.25 + 5x + x2 = 120 + 6.25

Combine like terms: 120 + 6.25 = 126.25
6.25 + 5x + x2 = 126.25

Factor a perfect square on the left side:
(x + 2.5)(x + 2.5) = 126.25

Calculate the square root of the right side: 11.236102527

Break this problem into two subproblems by setting 
(x + 2.5) equal to 11.236102527 and -11.236102527.

Subproblem 1
x + 2.5 = 11.236102527

Simplifying
x + 2.5 = 11.236102527

Reorder the terms:
2.5 + x = 11.236102527

Solving
2.5 + x = 11.236102527

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-2.5' to each side of the equation.
2.5 + -2.5 + x = 11.236102527 + -2.5

Combine like terms: 2.5 + -2.5 = 0.0
0.0 + x = 11.236102527 + -2.5
x = 11.236102527 + -2.5

Combine like terms: 11.236102527 + -2.5 = 8.736102527
x = 8.736102527

Simplifying
x = 8.736102527

Subproblem 2
x + 2.5 = -11.236102527

Simplifying
x + 2.5 = -11.236102527

Reorder the terms:
2.5 + x = -11.236102527

Solving
2.5 + x = -11.236102527

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-2.5' to each side of the equation.
2.5 + -2.5 + x = -11.236102527 + -2.5

Combine like terms: 2.5 + -2.5 = 0.0
0.0 + x = -11.236102527 + -2.5
x = -11.236102527 + -2.5

Combine like terms: -11.236102527 + -2.5 = -13.736102527
x = -13.736102527

Simplifying
x = -13.736102527

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {8.736102527, -13.736102527}
Solution
x = {8.736102527, -13.736102527}