1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding directional deriviative

  1. Oct 27, 2011 #1
    1. The problem statement, all variables and given/known data
    Find the directional derivative of f at P in the direction of a
    f(x,y)=(x*e^y)-(y*e^x); P(0,0);a=5i-2j

    my answer came out to 0


    3. The attempt at a solution

    i got the unit vector from p to a, which came out to <5/√(29),-2/√(29))
    and also the partial derivatives
    i then took the gradient of f and got <0,0>
    and then the directional derivative which came out to 0, is this right?
     
  2. jcsd
  3. Oct 27, 2011 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    "Directional vector from p to a" is meaningless. a is not a point- it is already the vector giving the direction. Just divide it by its length to get a unit vector.

    The gradient vector, at (0, 0), is NOT 0. Do it again. What do you get for the gradient before you set x= 0, y= 0?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Finding directional deriviative
  1. Deriviative of a log (Replies: 3)

  2. Complex Deriviative (Replies: 2)

Loading...