x=5.8*(0.40-x)*(0.30-x)

Solution for x=5.8*(0.40-x)*(0.30-x) equation:

Simplifying
x = 5.8(0.40 + -1x)(0.30 + -1x)

Multiply (0.40 + -1x) * (0.30 + -1x)
x = 5.8(0.40(0.30 + -1x) + -1x * (0.30 + -1x))
x = 5.8((0.30 * 0.40 + -1x * 0.40) + -1x * (0.30 + -1x))
x = 5.8((0.12 + -0.4x) + -1x * (0.30 + -1x))
x = 5.8(0.12 + -0.4x + (0.30 * -1x + -1x * -1x))
x = 5.8(0.12 + -0.4x + (-0.3x + 1x2))

Combine like terms: -0.4x + -0.3x = -0.7x
x = 5.8(0.12 + -0.7x + 1x2)
x = (0.12 * 5.8 + -0.7x * 5.8 + 1x2 * 5.8)
x = (0.696 + -4.06x + 5.8x2)

Solving
x = 0.696 + -4.06x + 5.8x2

Solving for variable 'x'.

Reorder the terms:
-0.696 + x + 4.06x + -5.8x2 = 0.696 + -4.06x + 5.8x2 + -0.696 + 4.06x + -5.8x2

Combine like terms: x + 4.06x = 5.06x
-0.696 + 5.06x + -5.8x2 = 0.696 + -4.06x + 5.8x2 + -0.696 + 4.06x + -5.8x2

Reorder the terms:
-0.696 + 5.06x + -5.8x2 = 0.696 + -0.696 + -4.06x + 4.06x + 5.8x2 + -5.8x2

Combine like terms: 0.696 + -0.696 = 0.000
-0.696 + 5.06x + -5.8x2 = 0.000 + -4.06x + 4.06x + 5.8x2 + -5.8x2
-0.696 + 5.06x + -5.8x2 = -4.06x + 4.06x + 5.8x2 + -5.8x2

Combine like terms: -4.06x + 4.06x = 0.00
-0.696 + 5.06x + -5.8x2 = 0.00 + 5.8x2 + -5.8x2
-0.696 + 5.06x + -5.8x2 = 5.8x2 + -5.8x2

Combine like terms: 5.8x2 + -5.8x2 = 0.0
-0.696 + 5.06x + -5.8x2 = 0.0

Begin completing the square.  Divide all terms by
-5.8 the coefficient of the squared term: 

Divide each side by '-5.8'.
0.12 + -0.8724137931x + x2 = 0

Move the constant term to the right:

Add '-0.12' to each side of the equation.
0.12 + -0.8724137931x + -0.12 + x2 = 0 + -0.12

Reorder the terms:
0.12 + -0.12 + -0.8724137931x + x2 = 0 + -0.12

Combine like terms: 0.12 + -0.12 = 0.00
0.00 + -0.8724137931x + x2 = 0 + -0.12
-0.8724137931x + x2 = 0 + -0.12

Combine like terms: 0 + -0.12 = -0.12
-0.8724137931x + x2 = -0.12

The x term is -0.8724137931x.  Take half its coefficient (-0.4362068966).
Square it (0.1902764566) and add it to both sides.

Add '0.1902764566' to each side of the equation.
-0.8724137931x + 0.1902764566 + x2 = -0.12 + 0.1902764566

Reorder the terms:
0.1902764566 + -0.8724137931x + x2 = -0.12 + 0.1902764566

Combine like terms: -0.12 + 0.1902764566 = 0.0702764566
0.1902764566 + -0.8724137931x + x2 = 0.0702764566

Factor a perfect square on the left side:
(x + -0.4362068966)(x + -0.4362068966) = 0.0702764566

Calculate the square root of the right side: 0.26509707

Break this problem into two subproblems by setting 
(x + -0.4362068966) equal to 0.26509707 and -0.26509707.

Subproblem 1
x + -0.4362068966 = 0.26509707

Simplifying
x + -0.4362068966 = 0.26509707

Reorder the terms:
-0.4362068966 + x = 0.26509707

Solving
-0.4362068966 + x = 0.26509707

Solving for variable 'x'.

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

Add '0.4362068966' to each side of the equation.
-0.4362068966 + 0.4362068966 + x = 0.26509707 + 0.4362068966

Combine like terms: -0.4362068966 + 0.4362068966 = 0.0000000000
0.0000000000 + x = 0.26509707 + 0.4362068966
x = 0.26509707 + 0.4362068966

Combine like terms: 0.26509707 + 0.4362068966 = 0.7013039666
x = 0.7013039666

Simplifying
x = 0.7013039666

Subproblem 2
x + -0.4362068966 = -0.26509707

Simplifying
x + -0.4362068966 = -0.26509707

Reorder the terms:
-0.4362068966 + x = -0.26509707

Solving
-0.4362068966 + x = -0.26509707

Solving for variable 'x'.

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

Add '0.4362068966' to each side of the equation.
-0.4362068966 + 0.4362068966 + x = -0.26509707 + 0.4362068966

Combine like terms: -0.4362068966 + 0.4362068966 = 0.0000000000
0.0000000000 + x = -0.26509707 + 0.4362068966
x = -0.26509707 + 0.4362068966

Combine like terms: -0.26509707 + 0.4362068966 = 0.1711098266
x = 0.1711098266

Simplifying
x = 0.1711098266

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {0.7013039666, 0.1711098266}