C(x)=0.001x^2+0.7x+10

Solution for C(x)=0.001x^2+0.7x+10 equation:

(C)=0.001C^2+0.7C+10

We move all terms to the left:

(C)-(0.001C^2+0.7C+10)=0

We get rid of parentheses

-0.001C^2+C-0.7C-10=0

We add all the numbers together, and all the variables

-0.001C^2+0.3C-10=0

a = -0.001; b = 0.3; c = -10;
Δ = b2-4ac
Δ = 0.32-4·(-0.001)·(-10)
Δ = 0.05
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{-(0.3)-\sqrt{0.05}}{2*-0.001}=\frac{-0.3-\sqrt{0.05}}{-0.002}
$
$C_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.3)+\sqrt{0.05}}{2*-0.001}=\frac{-0.3+\sqrt{0.05}}{-0.002}
$