1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Help with Volume of Revolution/Trig Substitution Problem

  1. Feb 24, 2014 #1
    1. The problem statement, all variables and given/known data

    The problem is attached in this post.

    2. Relevant equations

    The problem is attached in this post.

    3. The attempt at a solution

    Disk method with the radius equal to x/((x^2+3)^5/4)

    For Trig Substitution √(x^2+a^2) -> x=atanθ
    a=√3 -> a^2=3
    x=√(3)tanθ -> dx=√(3)sec^2(θ)

    Volume=π∫((3tan^2(θ)√(3)sec^2(θ))/(3tan^2(θ)+3)^5/4 from 0 to π/6

    I can't seem to simplify the integral to the point where I can get the answer etc.

    The answer is π/72

    Attached Files:

  2. jcsd
  3. Feb 24, 2014 #2


    User Avatar
    Science Advisor
    Homework Helper

    hi student93! :smile:

    (try using the X2 button just above the Reply box :wink:)

    i haven't checked, it's too difficult to read :redface:, but you seem to have inserted an extra tanθ somewhere …

    π∫((3tan(θ)√(3)sec2(θ))/(3tan2(θ)+3)5/4 can be simplified :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted