Hi,

I need to find the directional derivative of a function. I know how to do this, the problem with this particular question is that the point given is

$\displaystyle (x,y) not equal to (0,0)$

and the direction given is "toward the origin."

I know to find the directional derivative is simply using the dot product between the gradient of f and the unit vector, but I don't know how to determine what the unit vector here is exactly.

Oh, the function is

f(x,y) = ln sqrt(x^2 + y^2).

Thanks for your help!