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Homework Help: Directional derivatives, SIMPLE

  1. Sep 25, 2010 #1
    f(x, y, z) = xe^y + ye^z + ze^x, at (0, 0, 0),

    directional vector v = <-2, 0, 5>

    i solved for gradient f = (e^y + ze^x, xe^y + e^z, ye^z + e^x), at f(0,0,0) to be...

    gradient f = (1,1,1)

    this would make the answer just be -2 + 0 + 5 = 3
    but this isn't right.

    can someone show me what i did wrong?
     
  2. jcsd
  3. Sep 25, 2010 #2
  4. Sep 25, 2010 #3

    fzero

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    The directional derivative involves the unit vector in the direction of v, not v itself. Find the unit vector u = v/|v| and use that in your calculation.
     
  5. Sep 25, 2010 #4
    thank you! that makes a lot of sense
     
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