r2-400=0

Solution for r2-400=0 equation:

r2-400=0

We add all the numbers together, and all the variables

r^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:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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