Let $f ( x , y ) = x y ^ { 2 } + x ^ { 2 }$

Multiple Choice

Let $f ( x , y ) = x y ^ { 2 } + x ^ { 2 }$ . Then the maximum value of the directional derivative $D _ { \mathrm { u } } f ( - 1,2 )$ is

A) $\sqrt { 5 }$
B) $2 \sqrt { 3 }$
C) $2 \sqrt { 5 }$
D) $\sqrt { 35 }$
E) 5