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Math Help - Made the substitution, but now how to integrate?

  1. #1
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    Made the substitution, but now how to integrate?

    Hi all.

    I started with this equation:

    \frac {dy}{dx}=tan^2(x+y)

    I made the substitution u = x+y and am now looking at this:

    \frac {du}{tan^2u+1} = dx

    How the heck do I integrate that left side?
    Thanks from HallsofIvy
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  2. #2
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    Re: Made the substitution, but now how to integrate?

    1+\tan^{2}A=\sec^{2}A,

    \frac{1}{\sec^{2}A}=\cos^{2}A=\frac{1}{2}(1+\cos2A  ).
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  3. #3
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    Re: Made the substitution, but now how to integrate?

    Oh! Durr, trig identities! Thanks.
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