0=20x-4x^2

Solution for 0=20x-4x^2 equation:

0=20x-4x^2

We move all terms to the left:

0-(20x-4x^2)=0

We add all the numbers together, and all the variables

-(20x-4x^2)=0

We get rid of parentheses

4x^2-20x=0

a = 4; b = -20; c = 0;
Δ = b2-4ac
Δ = -202-4·4·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20}{2*4}=\frac{0}{8}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20}{2*4}=\frac{40}{8}
=5
$