615=3.14r^2-4

Solution for 615=3.14r^2-4 equation:

615=3.14r^2-4

We move all terms to the left:

615-(3.14r^2-4)=0

We get rid of parentheses

-3.14r^2+4+615=0

We add all the numbers together, and all the variables

-3.14r^2+619=0

a = -3.14; b = 0; c = +619;
Δ = b2-4ac
Δ = 02-4·(-3.14)·619
Δ = 7774.64
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{7774.64}}{2*-3.14}=\frac{0-\sqrt{7774.64}}{-6.28}
=-\frac{\sqrt{}}{-6.28}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{7774.64}}{2*-3.14}=\frac{0+\sqrt{7774.64}}{-6.28}
=\frac{\sqrt{}}{-6.28}
$