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Homework Help: Integrate 4cos(n pi t)

  1. Nov 5, 2009 #1
    1. The problem statement, all variables and given/known data

    4*cos(n pi t) d(t)
    2. Relevant equations

    3. The attempt at a solution

    is it: [4sin(n pi t)]/n.pi


    [4t sin (n pi t)]/n.pi

    any help very much welcome.
  2. jcsd
  3. Nov 5, 2009 #2


    User Avatar
    Science Advisor

    What do you get if you differentiate those?

    [itex]\int cos(u)du= sin(u)+ C[/edit]. What should you let u be? What is du?
    Last edited by a moderator: Nov 6, 2009
  4. Nov 5, 2009 #3
    . What should you let u be? What is du?[/QUOTE]

    Thanks for your quick reply, but you have lost me
  5. Nov 5, 2009 #4
    would u = 4

    therefore du=0
  6. Nov 5, 2009 #5


    Staff: Mentor

    Nope. Try a different u.
  7. Nov 5, 2009 #6
    Look at your given and the general solution:

    [tex]\int 4cos(n\pi t) dt [/tex]

    [tex]\int cos(u)du = sin(u)+ C [/tex]

    Notice the similarity.
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