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Finding Volume using integration

by Mcbrown108
Tags: integration, volume
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Mcbrown108
#1
Jul3-08, 02:30 PM
P: 6
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.
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tiny-tim
#2
Jul3-08, 02:47 PM
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Quote Quote by Mcbrown108 View Post
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

V= pi*int(e^(1x)+2)^2) a=0 b=.9
Hi Mcbrown108!

Isn't that for rotation about the x-axis?
Mcbrown108
#3
Jul3-08, 02:49 PM
P: 6
Oh yeah. so then would i change my bounds to a=-.9 b=.9

Mcbrown108
#4
Jul3-08, 03:22 PM
P: 6
Finding Volume using integration

that doesnt seem to work either
tiny-tim
#5
Jul3-08, 03:47 PM
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Quote Quote by Mcbrown108 View Post
Oh yeah. so then would i change my bounds to a=-.9 b=.9
It's not your bounds that are wrong it's your discs.

Your discs should be "horizontal" discs, centred on the y-axis.
Mcbrown108
#6
Jul3-08, 04:08 PM
P: 6
So i should plug in the given x's to get y's for my bounds?
tiny-tim
#7
Jul3-08, 05:01 PM
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Quote Quote by Mcbrown108 View Post
So i should plug in the given x's to get y's for my bounds?
I've no idea what that means, but I'm going to guess the answer is "YES!!"

Go for it!


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