Um, yes I think so.

Yes: Basically, the given (two) equations allow you to express sin(x) as a multiple of sin(y), and cos(x) as a multiple of cos(y). Thus, by applying the addition formula to sin(x+y), i.e. sin(x+y)=sin(x) cos(y)+cos(x) sin(y), you can reduce both sides of the equality that you have to prove to a certain multiple of sin(y) and cos(y). Therefore you only have to check whether, in fact, both sides work out to be the exact same multiple of sin(y) and cos(y).like sin(x)= (1/2)sin(y)