Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Integration of sine problem

  1. Dec 16, 2011 #1
    I am having problem with integration of this

    This is what i tried
    ∫sinπt - sinπt(cos^2πt)

    ∫sinπt - ∫sinπt(cos^2πt)

    ... and got stuck
    cos^2t=(1/2)(1+cos2t) so cos^2πt=(1/2)(1+cos2π)
    ∫1/2(sinπt) - (1/2)(cos2π)(sinπt)
    and still got stuck
    I am not even sure this is the right method to solve that.
    I know it should be (cos^3πt)/(3π) - (cosπt)/π but cannot get there

    Any help is welcome
  2. jcsd
  3. Dec 16, 2011 #2
    [tex]\cos x=t[/tex]
  4. Dec 16, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    In my opinion, it's absolutely necessary to include the differential, in this case dt, along with integral symbol.

    Which integral are you having difficulty with?
    [itex]\displaystyle \int\sin(\pi t)\,dt[/itex]​
    [itex]\displaystyle \int\sin(\pi t)\,\cos^2(\pi t)\,dt\ ?[/itex]​

    For the second one, let u = cos(πt) , then du = _?_
  5. Dec 17, 2011 #4
    Great. That was quite easy. Thank you very much
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook