(0.20-x)(0.80-x)=0

Solution for (0.20-x)(0.80-x)=0 equation:

(0.20-x)(0.80-x)=0

We add all the numbers together, and all the variables

(-1x+0.2)(-1x+0.8)=0

We multiply parentheses ..

(+x^2-0.8x-0.2x+0.16)=0

We get rid of parentheses

x^2-0.8x-0.2x+0.16=0

We add all the numbers together, and all the variables

x^2-1x+0.16=0

a = 1; b = -1; c = +0.16;
Δ = b2-4ac
Δ = -12-4·1·0.16
Δ = 0.36
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{-(-1)-\sqrt{0.36}}{2*1}=\frac{1-\sqrt{0.36}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{0.36}}{2*1}=\frac{1+\sqrt{0.36}}{2}
$