4x(x-8)=20

Solution for 4x(x-8)=20 equation:

4x(x-8)=20

We move all terms to the left:

4x(x-8)-(20)=0

We multiply parentheses

4x^2-32x-20=0

a = 4; b = -32; c = -20;
Δ = b2-4ac
Δ = -322-4·4·(-20)
Δ = 1344
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1344}=\sqrt{64*21}=\sqrt{64}*\sqrt{21}=8\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-32)-8\sqrt{21}}{2*4}=\frac{32-8\sqrt{21}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-32)+8\sqrt{21}}{2*4}=\frac{32+8\sqrt{21}}{8}
$