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Parametric equations to find surface area

  1. Sep 5, 2013 #1
    1. The problem statement, all variables and given/known data
    Which of the following integrals represents the area of the surface obtained by rotating the parametric curve
    x=t-t^2
    y=(4/3)t^(3/2)
    1<t<2

    2. Relevant equations
    A = integral ( 2pi(y) * sqrt( 1+ (dy/dx)^2))dx


    3. The attempt at a solution
    I solved for dy/dx and got
    12(t^1/2) / (9-18t)
    and then plug (1-2t)dt in for dx
    and (4/3)t^3/2 for y

    If i plug these all in and algebra correctly will i get the correct answer?
    How do i include the information that it's being rotated around the x-axis into my equation?
     
  2. jcsd
  3. Sep 5, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    That should give the right answer. You can simplify your dy/dx, by the way.

    Your equation at (2.) takes care about that.
     
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