# rotational volume question

• Nov 20th 2009, 10:14 PM
yeshtikvah
rotational volume question
Hi all, here's my question:

Find the volume of the solid formed by rotating the region enclosed by
y=e^(2x) + 1, y=0, x=0, x=0.2

My attempt at a solution:
V = pi int{ x = 0 to 0.2} [ (e^(2x) + 1)^2 dx]
V= pi int{ x = 0 to 0.2} [ ( e^(4x) + 2 e^(2x) + 1) dx]
V= pi { x = 0 to 0.2} ( (1/4) e^(4x) + (2/2) e^(2x) + x)
V = pi ( [(1/4) e^(0.8) + e^(0.4) + 0.4] - [(1/4) + 1] )

This isn't the right answer though. I'd like to know what I did wrong so I can get credit here and do problems right in the future. Thanks!!!!!
• Nov 21st 2009, 02:55 AM
tonio
Quote:

Originally Posted by yeshtikvah
Hi all, here's my question:

Find the volume of the solid formed by rotating the region enclosed by
y=e^(2x) + 1, y=0, x=0, x=0.2

My attempt at a solution:
V = pi int{ x = 0 to 0.2} [ (e^(2x) + 1)^2 dx]
V= pi int{ x = 0 to 0.2} [ ( e^(4x) + 2 e^(2x) + 1) dx]
V= pi { x = 0 to 0.2} ( (1/4) e^(4x) + (2/2) e^(2x) + x)
V = pi ( [(1/4) e^(0.8) + e^(0.4) + 0.4] - [(1/4) + 1] )

This isn't the right answer though. I'd like to know what I did wrong so I can get credit here and do problems right in the future. Thanks!!!!!

All is correct but the last, usually easier, part of evaluation: it must be $\displaystyle \frac{1}{4}e^{0.8}+e^{0.4}+0.2 <<<===$ you put 0.4 instead...that's all the problem!

Tonio
• Nov 21st 2009, 08:26 AM
yeshtikvah
Thank you!
Yes, you're right that should have been .2!

I tried that answer, but the online homework still says it's wrong. (Doh)

This happened with another problem I KNOW i did right. At least I know I'm doing the problems the right way. I guess I'll have to see my teacher to see why our answers aren't giving me any darn credit.
• Nov 21st 2009, 09:01 AM
tonio
Quote:

Originally Posted by yeshtikvah
Yes, you're right that should have been .2!

I tried that answer, but the online homework still says it's wrong. (Doh)

This happened with another problem I KNOW i did right. At least I know I'm doing the problems the right way. I guess I'll have to see my teacher to see why our answers aren't giving me any darn credit.

I don't know where some of you guys study that you've to produce your homework ONLINE and/or check it with some online checker or whatever.
Anyway, check your result with a calculator..

Tonio

Ps. Im yesh tikvah az lo hakol avud...