47=r^2*3.14

Solution for 47=r^2*3.14 equation:

47=r^2*3.14

We move all terms to the left:

47-(r^2*3.14)=0

We get rid of parentheses

-r^2*3.14+47=0

Wy multiply elements

-3.14r^2+47=0

a = -3.14; b = 0; c = +47;
Δ = b2-4ac
Δ = 02-4·(-3.14)·47
Δ = 590.32
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{590.32}}{2*-3.14}=\frac{0-\sqrt{590.32}}{-6.28}
=-\frac{\sqrt{}}{-6.28}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{590.32}}{2*-3.14}=\frac{0+\sqrt{590.32}}{-6.28}
=\frac{\sqrt{}}{-6.28}
$