Find the maximum rate of change

  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. SammyS

    SammyS 9,131
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

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