C(x)=0.0025x^2+80x+10000

Solution for C(x)=0.0025x^2+80x+10000 equation:

(C)=0.0025C^2+80C+10000

We move all terms to the left:

(C)-(0.0025C^2+80C+10000)=0

We get rid of parentheses

-0.0025C^2+C-80C-10000=0

We add all the numbers together, and all the variables

-0.0025C^2-79C-10000=0

a = -0.0025; b = -79; c = -10000;
Δ = b2-4ac
Δ = -792-4·(-0.0025)·(-10000)
Δ = 6141
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{-(-79)-\sqrt{6141}}{2*-0.0025}=\frac{79-\sqrt{6141}}{-0.005}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-79)+\sqrt{6141}}{2*-0.0025}=\frac{79+\sqrt{6141}}{-0.005}
$