-80=5x^2-100x

Solution for -80=5x^2-100x equation:

-80=5x^2-100x

We move all terms to the left:

-80-(5x^2-100x)=0

We get rid of parentheses

-5x^2+100x-80=0

a = -5; b = 100; c = -80;
Δ = b2-4ac
Δ = 1002-4·(-5)·(-80)
Δ = 8400
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:

$\sqrt{\Delta}=\sqrt{8400}=\sqrt{400*21}=\sqrt{400}*\sqrt{21}=20\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(100)-20\sqrt{21}}{2*-5}=\frac{-100-20\sqrt{21}}{-10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(100)+20\sqrt{21}}{2*-5}=\frac{-100+20\sqrt{21}}{-10}
$