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    Can anyone explain what question 5 is actually asking for?

    I've worked out \nabla f(0,2)=2i+j

    and D_u f=(2,1)\cdot u

    The question says the derivative = 0 but is this the directional derivative or what? Does it want me to find a direction u?
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    Yeah, you need to find a direction. Remember it has to be a unit vector.
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    (Original post by around)
    Yeah, you need to find a direction. Remember it has to be a unit vector.
    But how would I do that. Is the question saying D_u f=0 ?
 
 
 
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Updated: February 10, 2010
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