Let $f ( x , y ) = 3 x ^ { 3 } + y ^ { 2 } - 9 x + 4 y$

Essay

Let $f ( x , y ) = 3 x ^ { 3 } + y ^ { 2 } - 9 x + 4 y$ . Find the direction at the origin in which $f ( x , y )$ is decreasing the fastest.