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Homework Help: Calc 3 directional derivative question

  1. Oct 22, 2005 #1
    The question asks:
    Find the directional derivative of f (x, y, z) = z ln (x/y) at (1, 1, 2) toward the point (2, 2, 1).

    What I did was find the distance between the two points to be the directional vector (i+j-k) and then I took the norm of the direction vector. so my unit vector = 1/sqrt(3) * u; then I found the gradient. From there, I found the scalar product of my unit vector and the gradient to get 0. Did I approach this problem right? Does that answer seem correct to you?
  2. jcsd
  3. Oct 23, 2005 #2


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    Seems allright to me :smile:
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