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Don't know how to approach this one

  1. Oct 24, 2004 #1
    Let f be a function satisfying f'(x) = -3xf(x), f(1) = 4 and lim x->infinity f(x) = 0.

    Evaluate integral of -3x*f(x)*dx between 1 and infinity.

    Does this have to do with using comparison properties or something? I really don't know where to start. Thanks for any help.
  2. jcsd
  3. Oct 25, 2004 #2
    [tex]\int -3xf(x) dx = \int f'(x) dx.[/tex]

    Surely you know how to integrate f'(x).
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