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    1. d/dx[(dy/dz)(cosx)]



    2. As x,y,z->0, (delta(x)delta(y))/delta(z) = 0 right? If only y and z -> 0, = delta(x)dy/dz?
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    Could you post a screenshot of the question itself.
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    (Original post by Vikingninja)
    Could you post a screenshot of the question itself.
    That's my question.
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    (Original post by AlmostNotable)
    1. d/dx[(dy/dz)(cosx)]
    Use the product rule.

    Please post your thoughts and working.

    For 2, please make your question clearer. Post the original question.
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    (Original post by notnek)
    Use the product rule.

    Please post your thoughts and working.

    For 2, please make your question clearer. Post the original question.
    (d2y/dx2)(dy/dx)(cosx)-(dy/dx)(sinx), where is the mistake?

    Original question : As x,y,z->0, (delta(x)delta(y))/delta(z) = 0 right? If only y and z -> 0, = delta(x)dy/dz?
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    (Original post by AlmostNotable)
    (d2y/dx2)(dy/dx)(cosx)-(dy/dx)(sinx), where is the mistake?
    It's nearly right but where did the 'z' go?
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    (Original post by notnek)
    It's nearly right but where did the 'z' go?
    (d2y/dz2)(dy/dx)(cosx)-(dy/dz)(sinx), where is the mistake now?
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    (Original post by AlmostNotable)
    (d2y/dz2)(dy/dx)(cosx)-(dy/dz)(sinx), where is the mistake now?
    By the chain rule:

    \displaystyle \frac{d}{dx}\left (\frac{dy}{dz} \right ) = \frac{d}{dz}\left(\frac{dy}{dz} \right ) \frac{dz}{dx} = \frac{d^2 y}{dz^2}\cdot \frac{dz}{dx}
 
 
 
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