-40(x^2-20x+85)=0

Solution for -40(x^2-20x+85)=0 equation:

-40(x^2-20x+85)=0

We multiply parentheses

-40x^2+800x-3400=0

a = -40; b = 800; c = -3400;
Δ = b2-4ac
Δ = 8002-4·(-40)·(-3400)
Δ = 96000
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:

$\sqrt{\Delta}=\sqrt{96000}=\sqrt{6400*15}=\sqrt{6400}*\sqrt{15}=80\sqrt{15}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(800)-80\sqrt{15}}{2*-40}=\frac{-800-80\sqrt{15}}{-80}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(800)+80\sqrt{15}}{2*-40}=\frac{-800+80\sqrt{15}}{-80}
$