20000=1600r2

Solution for 20000=1600r2 equation:

20000=1600r^2

We move all terms to the left:

20000-(1600r^2)=0

a = -1600; b = 0; c = +20000;
Δ = b2-4ac
Δ = 02-4·(-1600)·20000
Δ = 128000000
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:

$\sqrt{\Delta}=\sqrt{128000000}=\sqrt{64000000*2}=\sqrt{64000000}*\sqrt{2}=8000\sqrt{2}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-8000\sqrt{2}}{2*-1600}=\frac{0-8000\sqrt{2}}{-3200}
=-\frac{8000\sqrt{2}}{-3200}
=-\frac{5\sqrt{2}}{-2}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+8000\sqrt{2}}{2*-1600}=\frac{0+8000\sqrt{2}}{-3200}
=\frac{8000\sqrt{2}}{-3200}
=\frac{5\sqrt{2}}{-2}
$