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Homework Help: Find the maximum rate of change

  1. Feb 9, 2012 #1
    Find the maximum rate of change of the function f(x,y) = (3 y^5)/x at the point (1,2)

    First I took the gradient of f(x,y)=<-3y^5*x^-2,15y^4*x^-1>
    and took the pt <1/sqrt(5),2/sqrt(5)>
    Then <-3y^5*x^-2,15y^4*x^-1>*<1/sqrt(5),2/sqrt(5)>
    the answer i get is 171.73
    I'm not sure where my error is
  2. jcsd
  3. Feb 9, 2012 #2


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    Why not evaluate the gradient at the point (1, 2) ?
  4. Feb 9, 2012 #3
    Sorry I evaluated at the gradient(1,2)=<-96,240> and then <-96,240>*<1/sqrt(5),2/sqrt(5)>
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