Given That the Directional Derivative Of $f ( x , y )$

Short Answer

Given that the directional derivative of $f ( x , y )$ at the point $( - 1,2 )$ in the direction of $\{ 3 , - 4 \}$ is $- 10$ and that $| \nabla f ( - 1,2 ) | = 10$ , find $\nabla f ( - 1,2 )$ .