1. Limited time only! Sign up for a free 30min personal 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!

Diretional Derivative

  1. Nov 23, 2015 #1

    RaulTheUCSCSlug

    User Avatar
    Gold Member

    Having a melt down as I have done this problem twice now and my exam is tomorrow and I can't seem to figure it out anymore.... ugh.


    1. The problem statement, all variables and given/known data

    The depth of a lake at the point on the surface with coordinates (x, y ) is given by D(x, y ) = 100−4x 2 −y 2 . a) If a boat at the point (−1, 2) is sailing in the direction 4~i +~j, is the water getting deeper or shallower ?
    2. Relevant equations
    I know that I need to use the gradient and I am going to need to have the direction scaled to a unit vector.

    3. The attempt at a solution
    So I took the gradient of D(x,y), plugged in (-1,2) then dotted it with the unit vector of (4,1) the answer is supposed to be 28/sqrt(17) and I can't seem to get that answer.
     
  2. jcsd
  3. Nov 23, 2015 #2

    RaulTheUCSCSlug

    User Avatar
    Gold Member

    never mind, I just kept doing the unit vector wrong. Simple arithmetic mistake.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Diretional Derivative
  1. A derivative (Replies: 14)

  2. Derivative of: (Replies: 1)

  3. Derivative of (Replies: 2)

  4. Partial Derivatives (Replies: 4)

Loading...