(x+0.4)(x+1.6)=0

Solution for (x+0.4)(x+1.6)=0 equation:

Simplifying
(x + 0.4)(x + 1.6) = 0

Reorder the terms:
(0.4 + x)(x + 1.6) = 0

Reorder the terms:
(0.4 + x)(1.6 + x) = 0

Multiply (0.4 + x) * (1.6 + x)
(0.4(1.6 + x) + x(1.6 + x)) = 0
((1.6 * 0.4 + x * 0.4) + x(1.6 + x)) = 0
((0.64 + 0.4x) + x(1.6 + x)) = 0
(0.64 + 0.4x + (1.6 * x + x * x)) = 0
(0.64 + 0.4x + (1.6x + x2)) = 0

Combine like terms: 0.4x + 1.6x = 2x
(0.64 + 2x + x2) = 0

Solving
0.64 + 2x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '-0.64' to each side of the equation.
0.64 + 2x + -0.64 + x2 = 0 + -0.64

Reorder the terms:
0.64 + -0.64 + 2x + x2 = 0 + -0.64

Combine like terms: 0.64 + -0.64 = 0.00
0.00 + 2x + x2 = 0 + -0.64
2x + x2 = 0 + -0.64

Combine like terms: 0 + -0.64 = -0.64
2x + x2 = -0.64

The x term is 2x.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2x + 1 + x2 = -0.64 + 1

Reorder the terms:
1 + 2x + x2 = -0.64 + 1

Combine like terms: -0.64 + 1 = 0.36
1 + 2x + x2 = 0.36

Factor a perfect square on the left side:
(x + 1)(x + 1) = 0.36

Calculate the square root of the right side: 0.6

Break this problem into two subproblems by setting 
(x + 1) equal to 0.6 and -0.6.

Subproblem 1
x + 1 = 0.6

Simplifying
x + 1 = 0.6

Reorder the terms:
1 + x = 0.6

Solving
1 + x = 0.6

Solving for variable 'x'.

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

Add '-1' to each side of the equation.
1 + -1 + x = 0.6 + -1

Combine like terms: 1 + -1 = 0
0 + x = 0.6 + -1
x = 0.6 + -1

Combine like terms: 0.6 + -1 = -0.4
x = -0.4

Simplifying
x = -0.4

Subproblem 2
x + 1 = -0.6

Simplifying
x + 1 = -0.6

Reorder the terms:
1 + x = -0.6

Solving
1 + x = -0.6

Solving for variable 'x'.

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

Add '-1' to each side of the equation.
1 + -1 + x = -0.6 + -1

Combine like terms: 1 + -1 = 0
0 + x = -0.6 + -1
x = -0.6 + -1

Combine like terms: -0.6 + -1 = -1.6
x = -1.6

Simplifying
x = -1.6

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {-0.4, -1.6}