90=1500r2

Solution for 90=1500r2 equation:

90=1500r^2

We move all terms to the left:

90-(1500r^2)=0

a = -1500; b = 0; c = +90;
Δ = b2-4ac
Δ = 02-4·(-1500)·90
Δ = 540000
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:

$\sqrt{\Delta}=\sqrt{540000}=\sqrt{90000*6}=\sqrt{90000}*\sqrt{6}=300\sqrt{6}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-300\sqrt{6}}{2*-1500}=\frac{0-300\sqrt{6}}{-3000}
=-\frac{300\sqrt{6}}{-3000}
=-\frac{\sqrt{6}}{-10}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+300\sqrt{6}}{2*-1500}=\frac{0+300\sqrt{6}}{-3000}
=\frac{300\sqrt{6}}{-3000}
=\frac{\sqrt{6}}{-10}
$