r*r=90000

Solution for r*r=90000 equation:

r*r=90000

We move all terms to the left:

r*r-(90000)=0

Wy multiply elements

r^2-90000=0

a = 1; b = 0; c = -90000;
Δ = b2-4ac
Δ = 02-4·1·(-90000)
Δ = 360000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{360000}=600$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-600}{2*1}=\frac{-600}{2}
=-300
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+600}{2*1}=\frac{600}{2}
=300
$