X(x-20)=5000

Solution for X(x-20)=5000 equation:

X(X-20)=5000

We move all terms to the left:

X(X-20)-(5000)=0

We multiply parentheses

X^2-20X-5000=0

a = 1; b = -20; c = -5000;
Δ = b2-4ac
Δ = -202-4·1·(-5000)
Δ = 20400
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:

$\sqrt{\Delta}=\sqrt{20400}=\sqrt{400*51}=\sqrt{400}*\sqrt{51}=20\sqrt{51}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20\sqrt{51}}{2*1}=\frac{20-20\sqrt{51}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20\sqrt{51}}{2*1}=\frac{20+20\sqrt{51}}{2}
$