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Help with an integral

  1. Jan 24, 2007 #1
    i have to integrate to find the electric potential due to a disk of charge with an uneven charge distribution. i was able to set up the intergral but i cant solve it. should i do integration by parts (i tried it) or use something else. just give me a hint

    int ( r^3/[(x^2 + r^2)]^.5) dr (x is a constant)

    thanks
     
  2. jcsd
  3. Jan 25, 2007 #2

    dextercioby

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    Make the substitution

    [tex] r=x\sinh t [/tex]

    Daniel.
     
  4. Jan 25, 2007 #3

    Gib Z

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    >.< I don't know Daniels way, Id go with trigonometric substitution, tan theta = r/x. Draw a triangle, you see that the hypotnuse is your denominator. Just solve for everything and sub them in, it reduces to [tex]x^3\int \tan^3 \theta \sec \theta d\theta[/tex].
     
  5. Jan 25, 2007 #4
    yea i figured it out. i did uv substitution, takeing u=r^2 and dx= r/(r^2+x^2) ^9.5)

    thank you for everyone who gave advice. :D
     
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