7000=3.1465*r^2

Solution for 7000=3.1465*r^2 equation:

7000=3.1465r^2

We move all terms to the left:

7000-(3.1465r^2)=0

We get rid of parentheses

-3.1465r^2+7000=0

a = -3.1465; b = 0; c = +7000;
Δ = b2-4ac
Δ = 02-4·(-3.1465)·7000
Δ = 88102
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:

$\sqrt{\Delta}=\sqrt{88102}=\sqrt{49*1798}=\sqrt{49}*\sqrt{1798}=7\sqrt{1798}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-7\sqrt{1798}}{2*-3.1465}=\frac{0-7\sqrt{1798}}{-6.293}
=-\frac{7\sqrt{1798}}{-6.293}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+7\sqrt{1798}}{2*-3.1465}=\frac{0+7\sqrt{1798}}{-6.293}
=\frac{7\sqrt{1798}}{-6.293}
$