Have you tried subbing in the definitions on each side?
I'm going through a past paper for an exam and found a problem which I don't know how to do, I am not sure if it is still examined any more but I am still interested in how you work it out:
Using definitions and
I think that it is related to double angle formula but I might be mistaken.
Well I stuck the terms in but they seem to cancel out each other so I assume I'm doing something wrong. Heres what I've done so far.
I then did the same for the ones with the y and got.
When i multiplied out i got:
and surely these terms all just cancel out, so where am I going wrong