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Math Help - scalar/vector field question

  1. #1
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    scalar/vector field question

    hey guys, I've been asked to consider the scalar field:

    f(x,y,z) = xy + xz + yz

    After finding grad f, I am asked to find the directional derivative of f at the point P (1,1,1) along the vector field u = [2,-1,1].

    What confuses me is finding the directional derivative of f along the vector field u... do i just calculate the dot product of grad f and the unit vector of u?

    grad f = (y+z)i + (x+z)j + (x+y)k

    The answer i got when performing the calculations the way I believe to be correct is 2\sqrt{6}/3, does anybody know if this is correct?
    Last edited by ben08; March 28th 2008 at 11:11 PM.
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  2. #2
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    Correct Answer is:

    It seems you are doing advanced engineering maths A at monash university ... sucks to be you ... and me.

    Well the answer I got was a little bit different to yours, I got 4/sqrt(6).

    Have you dont question 3?
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  3. #3
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    we have the same answer :P i've done question 3, look in my other posts and you'll find the solutions
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