Find the Directional Derivative to the Given Function at the Specified

Essay

Find the directional derivative to the given function at the specified point $P$ in the direction of the vector $\vec { u }$ $f ( x , y , z ) = x ^ { 2 } + y ^ { 2 } + z ^ { 2 } , P = ( 1,2,3 ) , \vec { u } = \left\langle \frac { \sqrt { 2 } } { 2 } , \frac { \sqrt { 2 } } { 2 } , 0 \right\rangle$