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Math Help - please help with a substitution problem

  1. #1
    Junior Member
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    please help with a substitution problem

    Evaluate the indefinite integral. (Enter your answer in terms of cos function.)



    so far i have:

    u = 4 pit
    du = pidt

    1/ pidu = dt

    once you subsitute it all back in i get a final answer of:

    (1/ pi)(cos4 pit)+c

    but this is not correct....
    where is my mistake?
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  2. #2
    Newbie Riyzar's Avatar
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    Quote Originally Posted by rhcp1231 View Post
    Evaluate the indefinite integral. (Enter your answer in terms of cos function.)



    so far i have:

    u = 4 pit
    du = pidt -> False

    1/ pidu = dt

    once you subsitute it all back in i get a final answer of:

    (1/ pi)(cos4 pit)+c

    but this is not correct....
    where is my mistake?
    (4\pi*t)' = 4\pi

    Also note that \int sin(u)du=-cos(u)+C
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  3. #3
    Junior Member
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    Quote Originally Posted by Riyzar View Post
    (4\pi*t)' = 4\pi

    Also note that \int sin(u)du=-cos(u)+C

    so is the answer:

    -1/pi(cos(pi*t))+c
    correct?
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  4. #4
    MHF Contributor
    skeeter's Avatar
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    Quote Originally Posted by rhcp1231 View Post
    so is the answer:

    -1/pi(cos(pi*t))+c
    correct?
    ... you're forgetting the 4.

    -\frac{\cos(4\pi t)}{4\pi} + C
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