(0.80-x)(0.20-x)=1

Solution for (0.80-x)(0.20-x)=1 equation:

(0.80-x)(0.20-x)=1

We move all terms to the left:

(0.80-x)(0.20-x)-(1)=0

We add all the numbers together, and all the variables

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

We multiply parentheses ..

(+x^2-0.2x-0.8x+0.16)-1=0

We get rid of parentheses

x^2-0.2x-0.8x+0.16-1=0

We add all the numbers together, and all the variables

x^2-1x-0.84=0

a = 1; b = -1; c = -0.84;
Δ = b2-4ac
Δ = -12-4·1·(-0.84)
Δ = 4.36
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{4.36}}{2*1}=\frac{1-\sqrt{4.36}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{4.36}}{2*1}=\frac{1+\sqrt{4.36}}{2}
$