having some trouble with proving identities, problem is:

sec2x = sec^2(x) / 2-sec^2(x) and the second one is

tany = sin2y / 1+cos2y

much help is appreciated

start with the definition of sec and tan in terms of sin, cos

then all that you need are the identities for double angles of sin and cos

which side should i start with the left or the right?

I would start from the right side and use the half-angle formulae instead.

I would start from the right side and use the half-angle formulae instead.

I start from the left-hand side by using double angle formula then divide both side by (cosx)^2