#tan^2(1/2 theta)=(tan theta-sin theta)/(tan theta + sin theta)#
Right Side #=(tan theta-sin theta)/(tan theta + sin theta)#
#=(sin theta / cos theta -sin theta)/(sin theta/cos theta + sin theta)#
#=((sin theta-sin theta cos theta) / cos theta) / ((sin theta+sin theta cos theta)/cos theta)#
#=(sin theta-sin theta cos theta) / cos theta * cos theta/(sin theta+sin theta cos theta)#
#=(sin theta-sin theta cos theta)/(sin theta+sin theta cos theta)#
#=(sin theta(1-cos theta))/(sin theta(1+cos theta))#
#=(1-cos theta)/(1+cos theta)#
#=(tan (1/2 theta))^2#
#=tan^2(1/2 theta)#
#=# Left Side