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Trig Integration

  1. Mar 26, 2007 #1
    1. The problem statement, all variables and given/known data

    [tex]\int_\frac{dx}{(4+x^2)^2}dx[/tex]

    2. Relevant equations



    3. The attempt at a solution

    SO....I started by making [tex]x = 2*tan x[/tex] and [tex]dx = 2*sec(x)^2[/tex]. The x is supposed to be the 0 sign with the line through it, but I don't know how to make that.

    I then made the equation [tex]\int \frac{2*sec(x)^2}{(4+2*tan(x)^2}*2*sec(x)^2[/tex]. I multiplied the two secants to get [tex]4*sec(x)^4[/tex] on the top, and then I turned the [tex]2*tan(x)^2[/tex] on the bottom into [tex]2*sec(x)^2-2[/tex]. The equation now looks like [tex]\int \frac{4*sec(x)^4}{(4+2*sec(x)^2-2}[/tex]. How does this simplify? I want to get rid of the [/tex]2*sec(x)^2[/tex] by dividing it with the top thing, but I don't think I can do that becaause of the -2 attached to it.
     
    Last edited: Mar 26, 2007
  2. jcsd
  3. Mar 26, 2007 #2
    you should fix your latex formatting.

    your integral becomes cos²(x).

    Show your work again, and let us know if you get stuck.
     
  4. Mar 27, 2007 #3

    dextercioby

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    [tex] \int \left(\frac{1}{-2x}\right)\left(\frac{-2x}{(4+x^2)^2}{}dx\right)=-\frac{1}{2x}\cdot\frac{1}{4+x^2}+\frac{1}{2}\int \frac{dx}{x^2 (4+x^2)} [/tex]

    [tex] =-\frac{1}{2x}\cdot\frac{1}{4+x^2}+\frac{1}{8}\int \left(\frac{1}{x^2}-\frac{1}{4+x^2}\right){}dx [/tex]

    ...
     
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