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chain rule du/dx in terms of dy/dx

07-04-2012 08:02PM

#1

joeperry

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Join Date: April 2008

Posts: 456

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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Comments

#2 07-04-2012 10:03PM

MathsManiac

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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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