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For x∈R^n define g:R->R by g(t)=f(tx) g'(t)?

  1. Sep 24, 2006 #1
    Have to use chain rule, so I was thinking,
    if we let u(t)=tx where x is the vector,
    then g(t)=f(u(t)) so dg(t)/dt=d(f u)(t)/dt=(df(t)/dt)u(t)+f(t)(du(t)/dt)
    but then I don't know what to do...
  2. jcsd
  3. Sep 25, 2006 #2


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    Please state the problme clearly. Is x a constant vector? What is f?

    What you have stated is not the chain rule- it looks more like the product rule. f(u(t)) is not "f u".

    dg(t)/dt= (df/du)(du/dt).
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