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Homework Help: Find the integral of xcos5x dx

  1. Jan 24, 2008 #1
    1. The problem statement, all variables and given/known data
    Find the integral of xcos5x dx

    2. Relevant equations
    uv- (integral)vdu

    3. The attempt at a solution

    I tried to pick u=cos5x and dv=xdx, but the book uses u=x, dv=cos5x dx

    Why can't my way work?
  2. jcsd
  3. Jan 24, 2008 #2


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    Science Advisor
    Homework Helper

    It can. Generally, people choose the [itex]u[/itex] and [itex]v[/itex] so that the problem is simplified - the way the book chooses makes the integrand more tractable.
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