Prove the identity
sin2x/1-cos2x = cotx
sin2x / [ 1 - cos 2x ] = cot x
[2 sinx cos x ] / [ 1 - (1 - 2sin^2x) ]
[ 2 sinx cosx ] / [ 2sin^2 x]
{2 cos x ] / [ 2 sin x ]
cos x / sin x = cot x