(3.14)(r2)=78.5

Solution for (3.14)(r2)=78.5 equation:

(3.14)(r2)=78.5

We move all terms to the left:

(3.14)(r2)-(78.5)=0

We add all the numbers together, and all the variables

(3.14)r2-78.5=0

We multiply parentheses

3.14r^2-78.5=0

a = 3.14; b = 0; c = -78.5;
Δ = b2-4ac
Δ = 02-4·3.14·(-78.5)
Δ = 985.96
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{985.96}}{2*3.14}=\frac{0-\sqrt{985.96}}{6.28}
=-\frac{\sqrt{}}{6.28}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{985.96}}{2*3.14}=\frac{0+\sqrt{985.96}}{6.28}
=\frac{\sqrt{}}{6.28}
$