36=3.1415(r^2)

Solution for 36=3.1415(r^2) equation:

36=3.1415(r^2)

We move all terms to the left:

36-(3.1415(r^2))=0

We get rid of parentheses

-3.1415r^2+36=0

a = -3.1415; b = 0; c = +36;
Δ = b2-4ac
Δ = 02-4·(-3.1415)·36
Δ = 452.376
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-\sqrt{452.376}}{2*-3.1415}=\frac{0-\sqrt{452.376}}{-6.283}
=-\frac{\sqrt{}}{-6.283}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{452.376}}{2*-3.1415}=\frac{0+\sqrt{452.376}}{-6.283}
=\frac{\sqrt{}}{-6.283}
$