Question

Sin2x/1-Cos2x

Answer 1

You need two identities:
sin2A = sinAcosA and
cos2A = 1 - 2sin^2A

so Sin2x/(1-Cos2x)
= 2sinxcosx/(1 - (1-2sin^2x))
= 2sinxcosx/(2sin^2x)
= cosx/sinx
= cotx