Question

Find a formula expressing the radius r of a sphere as a function of its surface area

Answer 1

The surface area of a sphere :
$A=4 \pi r^2$

Solving this equation for r:

A/(4* pi) = r^2          apply sqrt to both sides:

r = sqrt [A/(4 pi)]

Then the radius of a sphere as a function of its surface area :
$r= \sqrt{ \frac{A}{4 \pi } }$

Hope you got the idea