Question

Which is the formula for the surface area of a sphere with radius r?

Answer 1

formula of surface area of sphere :4πr²

Answer 2

The area of a disk enclosed by a circle of radius R is Pi*R2.  

The formula for the circumference of a circle of radius R is 2*Pi*R.  

A simple calculus check reveals that the latter is the derivative of the former with respect to R.

Similarly, the volume of a ball enclosed by a sphere of radius R is (4/3)*Pi*R3.  

And the formula for the surface area of a sphere of radius R is 4*Pi*R2.  

And, you can check that the latter is the derivative of the former with respect to R.

hope this is useful for u.