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Homework Help: Frustating arc length problem

  1. Sep 7, 2009 #1
    1. The problem statement, all variables and given/known data

    find the arc length
    x=2e^t, y=e^-t, z=2t

    2. Relevant equations

    3. The attempt at a solution
    ds/dt=sqrt((4e^2t)+(e^-2t)+4)) dt
    =integral from 0 to 1 sqrt(4e^4t+4e^2t+1)/e^t
    sorry about the lack of latex, I have no idea how to integrate this function
  2. jcsd
  3. Sep 7, 2009 #2
    you have got it right.
    why not try splitting them out. Take out the power and apply linearity rule to each integrand?
  4. Sep 7, 2009 #3


    Staff: Mentor

    If you don't know LaTeX, at least use some spaces to make what you have written more readable.
    Don't you mean
    dr/dt = 2e^t i - e^(-t) j + 2k?
    Are you sure about the middle term in the radical above?
    Shouldn't your integrand be ds/dt * dt?
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