If $f ( r , \theta ) = r \sin \theta + r ^ { 2 } \tan ^ { 2 } \theta$

Essay

If $f ( r , \theta ) = r \sin \theta + r ^ { 2 } \tan ^ { 2 } \theta$ , find the partial derivative of $f$ with respect to $r$ and the partial derivative with respect to $\theta$ , both at the point $\left( - 4 , \frac { \pi } { 6 } \right)$ .