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Answer check, Hyperbolic trig identity (proof)

  1. Jul 24, 2007 #1
    1. The problem statement, all variables and given/known data
    Evaluate the integral:
    (int sign) Sech³xTanhx dx


    2. Relevant equations
    Derivative of Sechx = -(SechxTanhx)


    3. The attempt at a solution

    Rewrite as:
    Sech²xSechxTanhx

    U=sechx
    Du = -(SechxTanhx)dx
    -Du = SechxTanhx dx
    replace into integral

    -(integral sign) U²du

    Evaluate:
    -U³ / 3

    answer = -Sech³x / 3

    ??? It just seems like there should be more to it. What do you guys think?
     
  2. jcsd
  3. Jul 24, 2007 #2
    Indeed there is more to it - a constant of integration. :wink:
     
  4. Jul 24, 2007 #3
    grr :mad:

    Thanks :redface:
     
  5. Jul 28, 2007 #4

    dextercioby

    User Avatar
    Science Advisor
    Homework Helper

    it would have been much simpler if you had written everything in terms of sinh and cosh.

    My 2ç
     
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