Question

A circle has an area of 80 square centimeters. Which answer is closer to the measure of its radius?

Answer 1

Since the area of a circle is $S=\pi r^2$ $\Rightarrow$ $80=\pi r^2$.

Now we are going to divide each side by $\pi$.

$\frac{80}{\pi}=r^2 \\r=\pm\sqrt{\frac{80}{\pi}} \\r=\pm\frac{\sqrt{80}}{\sqrt{\pi}}\approx\pm5.05 \ cm$

Since the radius could not be negative $\Rightarrow$ your answer is positive $5.05 \ cm$.