Finding Volume using integration

[Mcbrown108]

Homework Statement

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

Homework Equations

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

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]

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]

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

 

[Mcbrown108]

that doesn't seem to work either

 

[tiny-tim]

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]

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

 

[tiny-tim]

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!