900=3.14r2

Solution for 900=3.14r2 equation:

900=3.14r^2

We move all terms to the left:

900-(3.14r^2)=0

We get rid of parentheses

-3.14r^2+900=0

a = -3.14; b = 0; c = +900;
Δ = b2-4ac
Δ = 02-4·(-3.14)·900
Δ = 11304
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:

$\sqrt{\Delta}=\sqrt{11304}=\sqrt{36*314}=\sqrt{36}*\sqrt{314}=6\sqrt{314}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{314}}{2*-3.14}=\frac{0-6\sqrt{314}}{-6.28}
=-\frac{6\sqrt{314}}{-6.28}
=-\frac{\sqrt{314}}{-1.04666666667}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{314}}{2*-3.14}=\frac{0+6\sqrt{314}}{-6.28}
=\frac{6\sqrt{314}}{-6.28}
=\frac{\sqrt{314}}{-1.04666666667}
$