Find the Directional Derivative Of $f ( x , y ) = x ^ { 3 } y + 5 x y ^ { 2 }$

question 106

Essay

Find the directional derivative of $f ( x , y ) = x ^ { 3 } y + 5 x y ^ { 2 }$ at the point (1, 1)in the direction of $3 \vec { i } + 5 \vec { j }$ .