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Related rates

  1. Aug 16, 2004 #1
    i dont really understand when you differentiate both sides of an equation to, for example, time.

    like, if you have tan(x)=y/50,
    you would get sec^2(x)dx/dt=1/50*(dy/dt)
    so does that mean when you differentiate both sides you find the derivative of the whole term and then multiply it by dwhatever/dt?

    the book im looking at is just a review for calculus, its only got a short sentence here about this, and its confusing
     
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  3. Aug 16, 2004 #2

    arildno

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    Well, both x and y are functions of time.
    Hence, you use the chain rule when differentiating the equation
     
  4. Aug 16, 2004 #3

    shmoe

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    Yes, use the chain rule like arildno mentioned. For the problem you gave, you are thinking of x and y as functions of t. You can make this more explicit by replacing "x" with "x(t)" and "y" with "y(t)". The differentiate w.r.t time as normal. When this dependance on t is understood, texts will sometimes supress the (t) part of the notation to make things neater, like the example you gave.
     
  5. Aug 17, 2004 #4
    oh my... lol thankyou :-p im new with calc-learnin it myself this summer-and managed to remember the chain rule wrong. haha thanks guys
     
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