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Math Help - Trig Differentation

  1. #1
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    Trig Differentation

    I need help to differentate these 2 questions. Thanks for your help in advance.

    y = sinx/1+cosx
    For this one, i tried the quotient rule and ended off with cosx + cos^2(x) + sin^2(x)/ 1+cosx^2 which is not the right answer.

    y = cos(sin2x)
    I tried product rule and for the wrong answer.
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  2. #2
    MHF Contributor matheagle's Avatar
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    The first one is correct IF you square the entire denominator.
    Then use cos^2(x) + sin^2(x)=1 AND reduce.
    You need the chain rule on the second one.
    Last edited by matheagle; March 31st 2009 at 09:15 PM.
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  3. #3
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by proski117 View Post
    I need help to differentate these 2 questions. Thanks for your help in advance.

    y = sinx/1+cosx
    For this one, i tried the quotient rule and ended off with cosx + cos^2(x) + sin^2(x)/ 1+cosx^2 which is not the right answer.

    y = cos(sin2x)
    I tried product rule and for the wrong answer.
    I used the quotient rule on number 1 and got \frac{1+cos(x)}{(1+cos(x))^2} = \frac{1}{1+cos(x)}
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  4. #4
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    can you guys show me how to do the second one? i dont know what im doing wrong when using the chain rule
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  5. #5
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by proski117 View Post
    can you guys show me how to do the second one? i dont know what im doing wrong when using the chain rule

    y = cos(sin2x)

    y' = -sin(sin(2x)) \times 2cos(2x) = -2sin(sin(2x))cos(2x)

    note that 2cos(2x) is the derivative of sin(2x)
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