Find the Unit Vectors $\mathbf { u }$ And $\mathbf { V }$

Essay

Find the unit vectors $\mathbf { u }$ and $\mathbf { V }$ for $f ( x , y ) = x ^ { 3 } + 3 y ^ { 2 }$ which describes the direction of maximal and minimal increase at $( 2,1 )$ on the level curve $f ( x , y ) = 11$ .