(2h-8)*h=20

Solution for (2h-8)*h=20 equation:

(2h-8)*h=20

We move all terms to the left:

(2h-8)*h-(20)=0

We multiply parentheses

2h^2-8h-20=0

a = 2; b = -8; c = -20;
Δ = b2-4ac
Δ = -82-4·2·(-20)
Δ = 224
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$h_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$h_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{224}=\sqrt{16*14}=\sqrt{16}*\sqrt{14}=4\sqrt{14}$
$h_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-4\sqrt{14}}{2*2}=\frac{8-4\sqrt{14}}{4}
$
$h_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+4\sqrt{14}}{2*2}=\frac{8+4\sqrt{14}}{4}
$