C=-x^2+820x+18,017

Solution for C=-x^2+820x+18,017 equation:

=-C^2+820C+18.017

We move all terms to the left:

-(-C^2+820C+18.017)=0

We get rid of parentheses

C^2-820C-18.017=0

a = 1; b = -820; c = -18.017;
Δ = b2-4ac
Δ = -8202-4·1·(-18.017)
Δ = 672472.068
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$C_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-820)-\sqrt{672472.068}}{2*1}=\frac{820-\sqrt{672472.068}}{2}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-820)+\sqrt{672472.068}}{2*1}=\frac{820+\sqrt{672472.068}}{2}
$