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Integration Problem

  1. Nov 20, 2009 #1
    How does one compute

    [tex]\int r^{3}\:\sqrt{r^{2}+1}\:dr[/tex]

    Does this involve double u sub or trig sub?

    Thanks in advance,
    Justin
     
  2. jcsd
  3. Nov 20, 2009 #2

    tiny-tim

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    Hi Justin! :smile:

    (have a square-root: √ and an integral : ∫ and try using the X2 tag just above the Reply box :wink:)

    trig sub is probably easiest.

    (alternative hint: write it ∫ r(r2)(r2 + 1)1/2 dr :wink:)
     
  4. Nov 20, 2009 #3

    HallsofIvy

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    I would think the second was easiest: Let [itex]u= r^2+ 1[/itex]. Then du= 2rdr and [itex]r^2= u- 1[/itex]. (A single u-substitution, not double.)
     
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