I need to calculate directional derivative for such scalar field:
$$u=y\ln(l+x^2)-\arctan z\;\text{ where }\;\vec \ell=2\vec i-3\vec j-2\vec k, \;\text{ and }\;M(0,1,1).$$
The question is - what should I do with the $\ell$ in the $u(x,y,z)$? Just put in $l=2-3-2=-3$?