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Math Help - Finding a derivative

  1. #1
    Newbie pocketasian's Avatar
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    Finding a derivative

    If y = cosx^2 - sinx^2, then what does y' equal?

    The answer is -2sin(2x), but how do you actually get this answer? I used the power and chain rules when solving it, but the answer I got isn't the same. Thanks.
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  2. #2
    MHF Contributor Drexel28's Avatar
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    Quote Originally Posted by pocketasian View Post
    If y = cosx^2 - sinx^2, then what does y' equal?

    The answer is -2sin(2x), but how do you actually get this answer? I used the power and chain rules when solving it, but the answer I got isn't the same. Thanks.
    \cos^2(x)-\sin^2(x)=\cos\left(2x\right).
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  3. #3
    Newbie pocketasian's Avatar
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    Oh, that's right, that's an identity. Thank you very much!
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