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Homework Help: Tangent function vector?

  1. Sep 10, 2009 #1
    Tangent function vector???

    1. The problem statement, all variables and given/known data

    i know the formula for this problem. My hw was to like 5 of these and got the other 4. now stuck on the algebra part. please take a look and let me know where to go from here.
    problem is
    consider the vector function given below:
    r(t) = <8sqrt(2)t, e^(-8t), e^(8t)> only the 2 in the x cordinate is square root
    find the unit tangen vector

    it will be r'(t) / |r'(t)|

    derivative of r(t) = 8sqrt(2) , -8e^(-8t) , 8e^(8t)

    then i get stuck on the magnitude of this. i know it is each component squared then square root of all them added togeather.
    i get

    128 + 64e^(-64t) + 64e^(64t)
    then square root this whole thing.

    im not sure how to simplify the whole e thing.
    any help would be great!!!!
  2. jcsd
  3. Sep 10, 2009 #2


    Staff: Mentor

    Re: Tangent function vector???

    I didn't see it at first, but |r'(t)| is incorrect. When you square e8t you don't get e64t; you get e16t.

    Also, you might want to keep in mind that (e8t + e-8t)2 = e16t + 2 + e-16t
  4. Sep 10, 2009 #3
    Re: Tangent function vector???

    ok thanks i got it now!!
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