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Homework Help: Chain rule find find dw/dt

  1. Oct 3, 2005 #1
    Suppose w = x/y + y/z

    x = exp(t), y=2+sin(5t), and z= 2+cos(7t)

    A.) Use the chain rule to find dw/dt as a function of x, y, z, and t. Do not rewrite x, y, and z in terms of t, and do not rewrite exp(t) as x. I got this one right, the answer is 1/y*exp(t) +(- x/y^2+1/z)*(5*cos(5t)) + (-y/z^2)*(-7sin(7t)).

    i need help on B.

    B.) Use part A to evaluate dw/dt when t=0
    i just plugged in zeros for t, but i get an answer with the variables y and z, which i shouldnt have. what am i suppose to do for this question?
  2. jcsd
  3. Oct 3, 2005 #2


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    Well x, y and z are functions of t aren't they? So when you set t=0, you've GOT to write x, y and z in terms of t, and then set t=0 in the resulting equation.
  4. Oct 3, 2005 #3
    yup, thanks alot
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