Results 1 to 2 of 2

Math Help - Real quick question about washers...

  1. #1
    Senior Member
    Joined
    Jan 2009
    Posts
    296

    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?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Jester's Avatar
    Joined
    Dec 2008
    From
    Conway AR
    Posts
    2,373
    Thanks
    48
    Quote Originally Posted by zhupolongjoe View Post
    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 2 \pi \int_1^e x \ln x \,dx .
    Last edited by Jester; September 22nd 2009 at 09:36 AM. Reason: added the 2
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. real quick question about factoring
    Posted in the Algebra Forum
    Replies: 4
    Last Post: October 29th 2010, 06:01 PM
  2. Real quick question about simplifying!
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: April 20th 2010, 03:21 AM
  3. Real quick simple question...
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: December 5th 2009, 06:43 AM
  4. real quick derivative question
    Posted in the Calculus Forum
    Replies: 2
    Last Post: November 8th 2007, 07:17 PM
  5. One real quick question
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 6th 2007, 03:03 PM

Search Tags


/mathhelpforum @mathhelpforum