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Homework Help: Integral sqrt(9x^2-1)

  1. Mar 15, 2010 #1
    using integration table evaluate the following integral sqrt(9x^2-1)

    I just need to know how to start this off, i tried u substitution:

    u=9x^2-1 du=18xdx integral:u^(1/2)du/18x. but I don't know how to get rid of the x,

    So then from there i tried to use from the integration table integral:udv = uv-(integral vdu)
    u=u^1/2 dv=1/18x du=u^(3/2)/(3/2) v=
    I didn't know how to go about that
  2. jcsd
  3. Mar 15, 2010 #2


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    Try a trig substitution.
  4. Mar 15, 2010 #3


    Staff: Mentor

    Since you explicitly said "using integration table," a trig substitution is probably not the way to go. I'm assuming your integration table has the following integral in it:
    [tex]\int \sqrt{x^2 - a^2} dx[/tex]

    Factor 9 out of the two terms in the radical to get 9(x^2 - 1/9).
    Bring a factor of 3 out of the radical, and outside the integral.
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