Solution:

RHS

= cot \frac{A}{2} - tan \frac{A}{2}

= \dfrac{cos \frac{A}{2} }{sin \frac{A}{2}} - \dfrac{sin \frac{A}{2} }{cos \frac{A}{2}}

= \dfrac{cos^2 \frac{A}{2} - sin^2 \frac{A}{2}}{sin \frac{A}{2} cos\frac{A}{2}

= \dfrac{cosA}{sin \frac{A}{2} cos\frac{A}{2} } × \dfrac{2}{2}

= \dfrac{2cosA}{2 cos\frac{A}{2} sin\frac{A}{2}}

= \dfrac{2cosA}{sinA}

= 2cotA

LHS