0.8x^2+3.2x+2.40=0

Solution for 0.8x^2+3.2x+2.40=0 equation:

Simplifying
0.8x2 + 3.2x + 2.40 = 0

Reorder the terms:
2.40 + 3.2x + 0.8x2 = 0

Solving
2.40 + 3.2x + 0.8x2 = 0

Solving for variable 'x'.

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

Divide each side by '0.8'.
3 + 4x + x2 = 0

Move the constant term to the right:

Add '-3' to each side of the equation.
3 + 4x + -3 + x2 = 0 + -3

Reorder the terms:
3 + -3 + 4x + x2 = 0 + -3

Combine like terms: 3 + -3 = 0
0 + 4x + x2 = 0 + -3
4x + x2 = 0 + -3

Combine like terms: 0 + -3 = -3
4x + x2 = -3

The x term is 4x.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4x + 4 + x2 = -3 + 4

Reorder the terms:
4 + 4x + x2 = -3 + 4

Combine like terms: -3 + 4 = 1
4 + 4x + x2 = 1

Factor a perfect square on the left side:
(x + 2)(x + 2) = 1

Calculate the square root of the right side: 1

Break this problem into two subproblems by setting 
(x + 2) equal to 1 and -1.

Subproblem 1
x + 2 = 1

Simplifying
x + 2 = 1

Reorder the terms:
2 + x = 1

Solving
2 + x = 1

Solving for variable 'x'.

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

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

Combine like terms: 2 + -2 = 0
0 + x = 1 + -2
x = 1 + -2

Combine like terms: 1 + -2 = -1
x = -1

Simplifying
x = -1

Subproblem 2
x + 2 = -1

Simplifying
x + 2 = -1

Reorder the terms:
2 + x = -1

Solving
2 + x = -1

Solving for variable 'x'.

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

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

Combine like terms: 2 + -2 = 0
0 + x = -1 + -2
x = -1 + -2

Combine like terms: -1 + -2 = -3
x = -3

Simplifying
x = -3

Solution
The solution to the problem is based on the solutions
from the subproblems.
x = {-1, -3}