-50=-5x^2+20x

Solution for -50=-5x^2+20x equation:

-50=-5x^2+20x

We move all terms to the left:

-50-(-5x^2+20x)=0

We get rid of parentheses

5x^2-20x-50=0

a = 5; b = -20; c = -50;
Δ = b2-4ac
Δ = -202-4·5·(-50)
Δ = 1400
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:

$\sqrt{\Delta}=\sqrt{1400}=\sqrt{100*14}=\sqrt{100}*\sqrt{14}=10\sqrt{14}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-10\sqrt{14}}{2*5}=\frac{20-10\sqrt{14}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+10\sqrt{14}}{2*5}=\frac{20+10\sqrt{14}}{10}
$