4x(x-4)=20

Solution for 4x(x-4)=20 equation:

4x(x-4)=20

We move all terms to the left:

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

We multiply parentheses

4x^2-16x-20=0

a = 4; b = -16; c = -20;
Δ = b2-4ac
Δ = -162-4·4·(-20)
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-16)-24}{2*4}=\frac{-8}{8}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-16)+24}{2*4}=\frac{40}{8}
=5
$