A(11)=3.14r^2

Solution for A(11)=3.14r^2 equation:

(11)=3.14A^2

We move all terms to the left:

(11)-(3.14A^2)=0

We get rid of parentheses

-3.14A^2+11=0

a = -3.14; b = 0; c = +11;
Δ = b2-4ac
Δ = 02-4·(-3.14)·11
Δ = 138.16
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-\sqrt{138.16}}{2*-3.14}=\frac{0-\sqrt{138.16}}{-6.28}
=-\frac{\sqrt{}}{-6.28}
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{138.16}}{2*-3.14}=\frac{0+\sqrt{138.16}}{-6.28}
=\frac{\sqrt{}}{-6.28}
$