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: Solids of revolution, y axis

  1. Mar 9, 2010 #1
    The area
    Is rotated about the y axis, bounded by y=1, x=0 and x=ln2 find the volume of the solid.

    And i am clearly making something wrong, so if anyone could verify my work.

    [tex]~ 2\pi\int_0^{ln2}x\cdot(1-(e^x-1)[/tex]

    u=x, du=1
    dv=e^x, v=e^x

    [tex]\int xe^x -2x= xe^x -e^x -x^2[/tex]
    [tex]e^x(x-1)-x^2\bigg|_0^{ln2} = 2\pi \cdot ln2-1 -(ln2)^2[/tex]

    The answer is supposed to be [tex]2\pi(ln2-1)^2[/tex]
  2. jcsd
  3. Mar 9, 2010 #2
    where did that 1 come from in your shell method formula?
  4. Mar 9, 2010 #3
    When you integrate you should obtain : 2*pi*(ln22-2*ln2+1)

    That then can be the factored to the book's answer.

    You lost a 2 with the ln2
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook