(2.8-x)(0.4-x)=0

Solution for (2.8-x)(0.4-x)=0 equation:

(2.8-x)(0.4-x)=0

We add all the numbers together, and all the variables

(-1x+2.8)(-1x+0.4)=0

We multiply parentheses ..

(+x^2-0.4x-2.8x+1.12)=0

We get rid of parentheses

x^2-0.4x-2.8x+1.12=0

We add all the numbers together, and all the variables

x^2-3.2x+1.12=0

a = 1; b = -3.2; c = +1.12;
Δ = b2-4ac
Δ = -3.22-4·1·1.12
Δ = 5.76
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-3.2)-\sqrt{5.76}}{2*1}=\frac{3.2-\sqrt{5.76}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3.2)+\sqrt{5.76}}{2*1}=\frac{3.2+\sqrt{5.76}}{2}
$