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-   -   The derivative of two functions (https://www.askmehelpdesk.com/showthread.php?t=525840)

  • Nov 14, 2010, 12:40 PM
    susus
    the derivative of two functions
    it looks easy but, I do not know what I did wrong:
    what is the derivative of f(x) = cosx -1/3(cos^3 x )
    the answer is -sin^3 x
    while I got -sinx+cos^2 x * sinx !

    and also with this :
    f(x) = 1/ (x+ sqr(x^2 +1))

  • Nov 14, 2010, 12:53 PM
    galactus

    Your solution is correct. Only in another form.

  • Dec 5, 2010, 01:06 PM
    wutang69
    My word! Have you never heard of trigonometric identities? Here's a link so you never run into that problem again. http://www.clarku.edu/~djoyce/trig/identities.html

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