- #1

the_dane

- 30

- 0

## Homework Statement

How do I find the surface area of a sphere (r=15) with integrals.

## Homework Equations

Surface area for cylinder and sphere A=4*pi*r

^{2}.

## The Attempt at a Solution

I draw the graph for y=f(x)=√(15

^{2}-x

^{2}). A circle for for positive y values which I rotate. I will create infinite many cylinders with the height dx and radius y. The surface area of those dA=2*pi*y*dx then. I know that √(15

^{2}-x

^{2}) so ∫dA=∫

_{[0,15]}(2*pi*√(15

^{2}-x

^{2}))dx. It's only a half sphere for I multiplie by 2.

If I calculate the value by 4*pi*r

^{2}. What is my mistake?