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I need to find the direction in the xy plane in which one should travel, starting from point (1,1), to obtain the most rapid rate of decrease of

[tex]f(x,y,z) = (x + y - 2)^2 + (3x - y - 6)^2[/tex]

now, [tex]\nabla f = (2(x+y-2), 2(3x-y-6))[/tex]

so I'm thinking now I have to find the the unti vector 'u' which would be the direction in question. Unfortunately I do not know how to go on from here.

Somehow maximise [tex]\nabla f \cdot u[/tex] (where 'u' is a unit vector, dunno how to do vectors properly in latex )

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# Directional Derivatives

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