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Homework Help: Another trig sub

  1. Feb 4, 2006 #1
    These trig subs are killing me. :yuck:

    [tex]\int\cos^5(x)dx[/tex]


    hints?
     
  2. jcsd
  3. Feb 4, 2006 #2

    George Jones

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    [tex]\cos^{5} x = \left(1 - \sin^2 x \right)^{2} \cos x[/tex]

    Regards,
    George
     
  4. Feb 4, 2006 #3
    Thanks George... I am slowly getting the hang of this. I appriciate your help.
     
  5. Feb 4, 2006 #4

    HallsofIvy

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    One of the first things you should have learned: if you have sine or cosine to an odd power, factor out one of them to use with the dx.

    cos5 x dx= (cos4 x)(cos x dx)
    = (cos2 x)2 (cos x dx)= (1- sin2 x)2(cos x dx)

    Now, let u= sin x.
     
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