x=(40-2x)(20-2x)(x)

Solution for x=(40-2x)(20-2x)(x) equation:

Simplifying
x = (40 + -2x)(20 + -2x)(x)

Reorder the terms for easier multiplication:
x = x(40 + -2x)(20 + -2x)

Multiply (40 + -2x) * (20 + -2x)
x = x(40(20 + -2x) + -2x * (20 + -2x))
x = x((20 * 40 + -2x * 40) + -2x * (20 + -2x))
x = x((800 + -80x) + -2x * (20 + -2x))
x = x(800 + -80x + (20 * -2x + -2x * -2x))
x = x(800 + -80x + (-40x + 4x2))

Combine like terms: -80x + -40x = -120x
x = x(800 + -120x + 4x2)
x = (800 * x + -120x * x + 4x2 * x)
x = (800x + -120x2 + 4x3)

Solving
x = 800x + -120x2 + 4x3

Solving for variable 'x'.

Combine like terms: x + -800x = -799x
-799x + 120x2 + -4x3 = 800x + -120x2 + 4x3 + -800x + 120x2 + -4x3

Reorder the terms:
-799x + 120x2 + -4x3 = 800x + -800x + -120x2 + 120x2 + 4x3 + -4x3

Combine like terms: 800x + -800x = 0
-799x + 120x2 + -4x3 = 0 + -120x2 + 120x2 + 4x3 + -4x3
-799x + 120x2 + -4x3 = -120x2 + 120x2 + 4x3 + -4x3

Combine like terms: -120x2 + 120x2 = 0
-799x + 120x2 + -4x3 = 0 + 4x3 + -4x3
-799x + 120x2 + -4x3 = 4x3 + -4x3

Combine like terms: 4x3 + -4x3 = 0
-799x + 120x2 + -4x3 = 0

Factor out the Greatest Common Factor (GCF), 'x'.
x(-799 + 120x + -4x2) = 0

Subproblem 1
Set the factor 'x' equal to zero and attempt to solve:

Simplifying
x = 0

Solving
x = 0

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

Simplifying
x = 0
Subproblem 2
Set the factor '(-799 + 120x + -4x2)' equal to zero and attempt to solve:

Simplifying
-799 + 120x + -4x2 = 0

Solving
-799 + 120x + -4x2 = 0

Begin completing the square.  Divide all terms by
-4 the coefficient of the squared term: 

Divide each side by '-4'.
199.75 + -30x + x2 = 0

Move the constant term to the right:

Add '-199.75' to each side of the equation.
199.75 + -30x + -199.75 + x2 = 0 + -199.75

Reorder the terms:
199.75 + -199.75 + -30x + x2 = 0 + -199.75

Combine like terms: 199.75 + -199.75 = 0.00
0.00 + -30x + x2 = 0 + -199.75
-30x + x2 = 0 + -199.75

Combine like terms: 0 + -199.75 = -199.75
-30x + x2 = -199.75

The x term is -30x.  Take half its coefficient (-15).
Square it (225) and add it to both sides.

Add '225' to each side of the equation.
-30x + 225 + x2 = -199.75 + 225

Reorder the terms:
225 + -30x + x2 = -199.75 + 225

Combine like terms: -199.75 + 225 = 25.25
225 + -30x + x2 = 25.25

Factor a perfect square on the left side:
(x + -15)(x + -15) = 25.25

Calculate the square root of the right side: 5.024937811

Break this problem into two subproblems by setting 
(x + -15) equal to 5.024937811 and -5.024937811.

Subproblem 1
x + -15 = 5.024937811

Simplifying
x + -15 = 5.024937811

Reorder the terms:
-15 + x = 5.024937811

Solving
-15 + x = 5.024937811

Solving for variable 'x'.

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

Add '15' to each side of the equation.
-15 + 15 + x = 5.024937811 + 15

Combine like terms: -15 + 15 = 0
0 + x = 5.024937811 + 15
x = 5.024937811 + 15

Combine like terms: 5.024937811 + 15 = 20.024937811
x = 20.024937811

Simplifying
x = 20.024937811

Subproblem 2
x + -15 = -5.024937811

Simplifying
x + -15 = -5.024937811

Reorder the terms:
-15 + x = -5.024937811

Solving
-15 + x = -5.024937811

Solving for variable 'x'.

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

Add '15' to each side of the equation.
-15 + 15 + x = -5.024937811 + 15

Combine like terms: -15 + 15 = 0
0 + x = -5.024937811 + 15
x = -5.024937811 + 15

Combine like terms: -5.024937811 + 15 = 9.975062189
x = 9.975062189

Simplifying
x = 9.975062189

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {20.024937811, 9.975062189}
Solution
x = {0, 20.024937811, 9.975062189}