1. ## Real quick question about washers...

There is the region bounded by y=ln x, y=0, x=1, and x=e.

I need the volume when this is revolved about y-axis.

This will be a washer...so I have that x=e^y and now I did.....

pi*integral (0 to 1) e^2-e^2y dy

Is this correct?

I put outer radius of e and inner of e^y...would that be correct?

2. Originally Posted by zhupolongjoe
There is the region bounded by y=ln x, y=0, x=1, and x=e.

I need the volume when this is revolved about y-axis.

This will be a washer...so I have that x=e^y and now I did.....

pi*integral (0 to 1) e^2-e^2y dy

Is this correct?

I put outer radius of e and inner of e^y...would that be correct?
Yes, it is correct. You could also have used shells and obtained $\displaystyle 2 \pi \int_1^e x \ln x \,dx$.