X(x-2)=720

Solution for X(x-2)=720 equation:

X(X-2)=720

We move all terms to the left:

X(X-2)-(720)=0

We multiply parentheses

X^2-2X-720=0

a = 1; b = -2; c = -720;
Δ = b2-4ac
Δ = -22-4·1·(-720)
Δ = 2884
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:

$\sqrt{\Delta}=\sqrt{2884}=\sqrt{4*721}=\sqrt{4}*\sqrt{721}=2\sqrt{721}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-2\sqrt{721}}{2*1}=\frac{2-2\sqrt{721}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+2\sqrt{721}}{2*1}=\frac{2+2\sqrt{721}}{2}
$