Finding Volume using integration

Mcbrown108

1. The problem statement, all variables and given/known data
Find the volume of the solid formed by rotating the region enclosed by:
(e^(1x)+2)/y=0/x=0/x=.9
about the y axis


2. Relevant equations
Probably disk method i would assume:
V=pi*int((f(x)^2) dx from bounds a to b


3. The attempt at a solution

V= pi*int(e^(1x)+2)^2) a=0 b=.9
v=pi*int(e^(2x)+4) a=0 b=.9
v=pi*(1/2e^(2x)+4x)
v=pi*(1/2e^(2(.9))-(1/2e^0)+(4(.9)
v=pi*(3.025)-(1/2)+3.6
v=6.125pi

But my answer is not correct.

tiny-tim

Hi Mcbrown108!

Isn't that for rotation about the x-axis?

Mcbrown108

Oh yeah. so then would i change my bounds to a=-.9 b=.9

Mcbrown108

that doesnt seem to work either

tiny-tim

It's not your bounds that are wrong … it's your discs.

Your discs should be "horizontal" discs, centred on the y-axis.

Mcbrown108

So i should plug in the given x's to get y's for my bounds?

tiny-tim

I've no idea what that means, but I'm going to guess the answer is … "YES!!"

Go for it!