5x^2-20x=90

Solution for 5x^2-20x=90 equation:

5x^2-20x=90

We move all terms to the left:

5x^2-20x-(90)=0

a = 5; b = -20; c = -90;
Δ = b2-4ac
Δ = -202-4·5·(-90)
Δ = 2200
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:

$\sqrt{\Delta}=\sqrt{2200}=\sqrt{100*22}=\sqrt{100}*\sqrt{22}=10\sqrt{22}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-10\sqrt{22}}{2*5}=\frac{20-10\sqrt{22}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+10\sqrt{22}}{2*5}=\frac{20+10\sqrt{22}}{10}
$