400=c2

Solution for 400=c2 equation:

400=c2

We move all terms to the left:

400-(c2)=0

We add all the numbers together, and all the variables

-1c^2+400=0

a = -1; b = 0; c = +400;
Δ = b2-4ac
Δ = 02-4·(-1)·400
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-40}{2*-1}=\frac{-40}{-2}
=+20
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+40}{2*-1}=\frac{40}{-2}
=-20
$