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chain rule du/dx in terms of dy/dx

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  • 07-04-2012 8:02pm
    #1
    joeperry
    Closed Accounts Posts: 527 ✭✭✭


    Hi i'm not sure how this works.

    Q1. u = cos(5y)

    So do i make y = 5y

    so then it's, dcos(y)/dx.dy/dx

    my answer is
    -5sin(5y)

    Is that correct please?


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    #2
    MathsManiac
    Registered Users Posts: 1,595 ✭✭✭MathsManiac


    What exactly is the question? Are you asked, as the title suggests, "Find du/dx in terms of dy/dx"?

    If so, then you're almost there. Since y is itself a function of x, there is a further instance of the chain rule at play. The answer is -5(sin(5y))(dy/dx).


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