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Math Help - derivatives

  1. #1
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    derivatives

    2cosx+2cos^2(x)
    =2cosx+2(cosx)^2

    differentiate
    =-2sinx-4sinx[cosx]'
    =-2sinx+4sin^2(x)

    but if i instead did
    2cosx+2cos^2(x)
    =2cosx+2cosxcosx

    use product rule
    =-4sinxcosx

    different answers. did i do something wrong in the first method? it worked perfectly on a different problem, but i got this one wrong.
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  2. #2
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    ok....i noticed i did this same thing on a different but very similar problem and got that one marked correct

    3cosx-3cos^2x

    differentiated first method
    =-3sinx-6sin^2x

    second method(product rule way)
    =-3sinx-3sinxcosx

    this whole thing is started to get me really frustrated. how the hell am i supposed to study correctly with all these correction mistakes...
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  3. #3
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    Re:

    Re: Just Relax
    Attached Thumbnails Attached Thumbnails derivatives-22.gif  
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  4. #4
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    yeah......sorry >< all this studying is getting to me

    i figured out what was wrong...first method doesnt really work...

    thanks
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