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Math Help - Quick Question.

  1. #1
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    Quick Question.

    What's happening in this derivative?

    -5e^{xcos(x)}

    Ends as:

    5*x*e^{x*cos(x)}*sin(x)-5*cos(x)*e^{x*cos(x)}

    From what I know.

    -5e^u*u'

    Does not get me to that end result, where u equals (x*cos(x)). Is there a special rule in ending with derivatives like this?
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  2. #2
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    Quote Originally Posted by Zanderist View Post
    -5e^u*u'

    Does not get me to that end result, where u equals (x*cos(x)). Is there a special rule in ending with derivatives like this?
    This formula is correct ..
    In your problem u=x \, cos(x) ..
    Apply the formula .. and notice that you will need the product rule to find u' ..
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  3. #3
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    oh right.
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  4. #4
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    BTW, you should put brackets like this:


    Quote Originally Posted by Zanderist View Post
    5xe^{xcos(x)} {\color{red} ( } sin(x)-5cos(x)e^{xcos(x)} {\color{red} ) }
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