(4-x)(x+1.4)=0

Solution for (4-x)(x+1.4)=0 equation:

Simplifying
(4 + -1x)(x + 1.4) = 0

Reorder the terms:
(4 + -1x)(1.4 + x) = 0

Multiply (4 + -1x) * (1.4 + x)
(4(1.4 + x) + -1x * (1.4 + x)) = 0
((1.4 * 4 + x * 4) + -1x * (1.4 + x)) = 0
((5.6 + 4x) + -1x * (1.4 + x)) = 0
(5.6 + 4x + (1.4 * -1x + x * -1x)) = 0
(5.6 + 4x + (-1.4x + -1x2)) = 0

Combine like terms: 4x + -1.4x = 2.6x
(5.6 + 2.6x + -1x2) = 0

Solving
5.6 + 2.6x + -1x2 = 0

Solving for variable 'x'.

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

Divide each side by '-1'.
-5.6 + -2.6x + x2 = 0

Move the constant term to the right:

Add '5.6' to each side of the equation.
-5.6 + -2.6x + 5.6 + x2 = 0 + 5.6

Reorder the terms:
-5.6 + 5.6 + -2.6x + x2 = 0 + 5.6

Combine like terms: -5.6 + 5.6 = 0.0
0.0 + -2.6x + x2 = 0 + 5.6
-2.6x + x2 = 0 + 5.6

Combine like terms: 0 + 5.6 = 5.6
-2.6x + x2 = 5.6

The x term is -2.6x.  Take half its coefficient (-1.3).
Square it (1.69) and add it to both sides.

Add '1.69' to each side of the equation.
-2.6x + 1.69 + x2 = 5.6 + 1.69

Reorder the terms:
1.69 + -2.6x + x2 = 5.6 + 1.69

Combine like terms: 5.6 + 1.69 = 7.29
1.69 + -2.6x + x2 = 7.29

Factor a perfect square on the left side:
(x + -1.3)(x + -1.3) = 7.29

Calculate the square root of the right side: 2.7

Break this problem into two subproblems by setting 
(x + -1.3) equal to 2.7 and -2.7.

Subproblem 1
x + -1.3 = 2.7

Simplifying
x + -1.3 = 2.7

Reorder the terms:
-1.3 + x = 2.7

Solving
-1.3 + x = 2.7

Solving for variable 'x'.

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

Add '1.3' to each side of the equation.
-1.3 + 1.3 + x = 2.7 + 1.3

Combine like terms: -1.3 + 1.3 = 0.0
0.0 + x = 2.7 + 1.3
x = 2.7 + 1.3

Combine like terms: 2.7 + 1.3 = 4
x = 4

Simplifying
x = 4

Subproblem 2
x + -1.3 = -2.7

Simplifying
x + -1.3 = -2.7

Reorder the terms:
-1.3 + x = -2.7

Solving
-1.3 + x = -2.7

Solving for variable 'x'.

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

Add '1.3' to each side of the equation.
-1.3 + 1.3 + x = -2.7 + 1.3

Combine like terms: -1.3 + 1.3 = 0.0
0.0 + x = -2.7 + 1.3
x = -2.7 + 1.3

Combine like terms: -2.7 + 1.3 = -1.4
x = -1.4

Simplifying
x = -1.4

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {4, -1.4}