900=1500r2

Solution for 900=1500r2 equation:

900=1500r^2

We move all terms to the left:

900-(1500r^2)=0

a = -1500; b = 0; c = +900;
Δ = b2-4ac
Δ = 02-4·(-1500)·900
Δ = 5400000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{5400000}=\sqrt{360000*15}=\sqrt{360000}*\sqrt{15}=600\sqrt{15}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-600\sqrt{15}}{2*-1500}=\frac{0-600\sqrt{15}}{-3000}
=-\frac{600\sqrt{15}}{-3000}
=-\frac{\sqrt{15}}{-5}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+600\sqrt{15}}{2*-1500}=\frac{0+600\sqrt{15}}{-3000}
=\frac{600\sqrt{15}}{-3000}
=\frac{\sqrt{15}}{-5}
$