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Math Help - Help with trig subs...

  1. #1
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    Help with trig subs...

    i cant seem to figure out what to sub in into the integral of x/(((x+2)^2)+9). PAny help greatly apprehiated asap.... Thanks!
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  2. #2
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    Quote Originally Posted by skater8705 View Post
    i cant seem to figure out what to sub in into the integral of x/(((x+2)^2)+9). PAny help greatly apprehiated asap.... Thanks!
    \int \frac{x}{\sqrt{(x+2)^2+9}} dx
    Let t=x+2 so,
    \int \frac{t-2}{\sqrt{t^2+9}} dt = \int \frac{t}{\sqrt{t^2+9}} dt - 2 \int \frac{1}{\sqrt{t^2+9}} dt
    The first integral use the substitution \xi = t^2 and the second is an inverse sine integral.
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  3. #3
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    Quote Originally Posted by skater8705 View Post
    i cant seem to figure out what to sub in into the integral of x/(((x+2)^2)+9).
    \int\frac x{(x+2)^2+9}\,dx.

    Define x+2=3\tan u\implies dx=3\sec^2u.

    Substitute and play with it.
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  4. #4
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    thanks for the responses... both methods seemed to get the same ans... thanks again!!!
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