72=2r^2

Solution for 72=2r^2 equation:

72=2r^2

We move all terms to the left:

72-(2r^2)=0

a = -2; b = 0; c = +72;
Δ = b2-4ac
Δ = 02-4·(-2)·72
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-24}{2*-2}=\frac{-24}{-4}
=+6
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+24}{2*-2}=\frac{24}{-4}
=-6
$