# Thread: Finding the surface area of a function

1. ## Finding the surface area of a function

I successfully did a problem like this before but I am stuck on this one.

Here is the question:
Find the area of the surface obtained by rotating the curve
from to about the -axis.

Any help would be greatly appreciated!
Thanks in advance!

2. Originally Posted by s3a
I successfully did a problem like this before but I am stuck on this one.

Here is the question:

Find the area of the surface obtained by rotating the curve

from to about the -axis.

Any help would be greatly appreciated!
Thanks in advance!
S = $2 \pi \int_0^4 x \sqrt{1+\left[ y' \right]^2} \, dx$ ..

3. Instead of x multiplying the square root, shouldn't it be (1+5x^2) multiplying the root?

Edit: you are right but why? I thought You only put y like that and that if the variables are x you have to put the whole equation in.

4. no because you're rotating about the "y" axis.