2x(x-10)=20

Solution for 2x(x-10)=20 equation:

2x(x-10)=20

We move all terms to the left:

2x(x-10)-(20)=0

We multiply parentheses

2x^2-20x-20=0

a = 2; b = -20; c = -20;
Δ = b2-4ac
Δ = -202-4·2·(-20)
Δ = 560
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:

$\sqrt{\Delta}=\sqrt{560}=\sqrt{16*35}=\sqrt{16}*\sqrt{35}=4\sqrt{35}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-4\sqrt{35}}{2*2}=\frac{20-4\sqrt{35}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+4\sqrt{35}}{2*2}=\frac{20+4\sqrt{35}}{4}
$