1. Nov 18, 2006

### team31

when u=-0.6i+0.8j, Du f(1,2)=? gradient f=(18,9)
I use unit vector dot (-0.6,0.8) dotted with the gradient f, which turns out to be -3.6
so here is the question. A: the maximum value of Dv f(1,2) is=?
B: this maximum occurs when v=(?,?)
I'm confued with the Dv thing. For my guess is that I should use (1,2) to creat a unit vector which is (1/sqrt5, 2/sqrt5), and use that unit vetor dotted with the gradient f, which gives me the maximum value of Dv f(1,2)
then i will find a vector that its dot product with ( 1/sqrt5, 2/sqrt5) is 0, and tha should be the direction of V which is the answer for part B

Am I doing this right? plaese help me out. I've been looking into my text book but couldn't find the symbol Dv, they all used Du. Thanks u