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Thread: Chain rule help

  1. #1
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    Chain rule help

    Can someone explain to me how we get the last line from the chain rule please?

    Thank you

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  2. #2
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    Re: Chain rule help

    You have:

    $\dfrac{dz}{d\tau} = \dfrac{dz}{d(1-\tau)}\dfrac{d(1-\tau)}{d\tau}$

    The derivative of $1-\tau$ with respect to $\tau$ is -1, so the second term is -1.
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  3. #3
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    Re: Chain rule help

    Quote Originally Posted by SlipEternal View Post
    You have:

    $\dfrac{dz}{d\tau} = \dfrac{dz}{d(1-\tau)}\dfrac{d(1-\tau)}{d\tau}$

    The derivative of $1-\tau$ with respect to $\tau$ is -1, so the second term is -1.
    Thanks! How come the first term doesn't change at all though? I thought with chain rule you have to take derivative of both functions?

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  4. #4
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    Re: Chain rule help

    You are "taking the derivative of both functions". $\frac{dz}{d(1- \tau)}$ is the first derivative and $\frac{d(1- \tau)}{d\tau}= -1$ is the second derivative.
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