# Math Help - Integration Help

1. ## Integration Help

What I think I need help with is (forgive my Latex ignorance):
. . ._____
√1+1/x dx

I have no idea how to integrate this.

In case I set up the integral wrong, the original question calls for evaluating the surface area of y=2√x rotated around the x-axis (on the interval from 4 to 9).

So first derivative (1/√x)
First derivative squared (1/x)

Into the form of (arc length x 2π):
. . . . ._____
√1+1/x dx (evaluated on aforementioned interval.)

2. $2{\pi}\int_{a}^{b}f(x)\sqrt{1+[f'(x)]^{2}}dx$. You forgot the f(x)

The surface area is given by $4{\pi}\int_{4}^{9}\sqrt{x}\sqrt{1+\frac{1}{x}}dx$

This simplifies down to $4{\pi}\int_{4}^{9}\sqrt{x+1}dx$

Now, can you integrate that. A little easier now?.

3. Oh yeah! Thanks!