In $\Delta ABC, \sum (b+c) \tan \large\frac{A}{2}$$ \tan \bigg(\large\frac{B-C}{2}\bigg)$ is equal to :

Question

\[\begin {array} {1 1} (a)\;a & \quad (b)\;b \\ (c)\;c & \quad (d)\;0 \end {array}\]