Question

is it right? I don't know how to remove this 2

Answer 1

oh! You made a blunder in the 3rd step of L.H.S and in the 2nd step of R.H.S

Actually

$after \\ \sin( \alpha ) \div ((1 + \cos( \alpha ) ) \div \sin( \alpha ) ) \\ it \: is \\ { \sin( \alpha ) }^{2} \div (1 + \cos( \alpha ) ) \: \: in \: l.h.s.$

and, in R.H.S.

$after \\ 2 + \sin( \alpha ) \div (( \cos( \alpha ) - 1) \div \sin( \alpha )) \\ it \: is \\ 2 + ({ \sin( \alpha ) }^{2} \div ( \cos( \alpha ) - 1))$

and the rest you can do all by yourself