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Simple u-du

  1. Sep 14, 2004 #1
    how would i find the anti-derv. of (cos(2x)). im really confused with sub.

    ok i'll use u-du

    u = 2x
    du = 2 dx
    dx = 1/2 du

    k so... cos(u)*dx

    since the dx is there, you plug in the dx that i found right? so... sin(2x)1/2

    ok so that's a simple integration problem, can someone give me a harder problem and show me how to find "dx", that's what im really confused about.
  2. jcsd
  3. Sep 14, 2004 #2


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    Homework Helper

    So if in general:
    u = f(x)
    du = f'(x) dx
    dx = du/f'(x)
    Find the anti-derivative of:
    cos(cos(x)) ⋅ sin(x)
    and use:
    u = cos(x)
    as a substitution.
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