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Homework Help: Integration cos theta help

  1. Dec 15, 2008 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    3. The attempt at a solution
    Let x=sintheta
    dx=cos theta
    Now I get stuck
  2. jcsd
  3. Dec 15, 2008 #2
    well, i believe

    [tex] sin^2x=\frac{1-cos2x}{2}[/tex] would help.
  4. Dec 15, 2008 #3


    Staff: Mentor

    You don't show dx in your original integral, but it should be there. You need to replace it and the square root in the denominator, using your substitution.

    In your substitution, dx = cos(theta) d(theta).
  5. Dec 15, 2008 #4


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    Science Advisor
    Homework Helper

    There's a trig formula that let's you express sin(theta)^2 in terms of cos(2*theta). Can you find it?
  6. Dec 15, 2008 #5
    so then i would make u=2x and du=2dx
  7. Dec 15, 2008 #6
    well first you woudl break it into 1/2-1/2 cos(2x) then if you want you can make that substituion, that would work.
  8. Dec 15, 2008 #7
    Ok, well that's what I meant.
  9. Dec 15, 2008 #8
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