The Student Room Group
Reply 1
LHS:

[e^A + e^-A]/2 + [e^B + e^-B]/2

RHS:

2 [e^(A+B)/2 + e^-(A+B)/2]/2 [e^(A-B)/2 + e^-(A-B)/2]/2

= 2 [e^A/2 e^B/2 + e^-A/2 e^-B/2]/2 [e^A/2 e^-B/2 + e^-A/2 e^B/2]/2

= 2 [e^A/2 e^A/2 e^B/2 e^-B/2 + e^-A/2 e^-A/2 e^-B/2 e^B/2 + e^A/2 e^-A/2 e^B/2 e^B/2 + e^-A/2 e^A/2 e^-B/2 e^-B/2]/4

= 2 [e^A + e^-A + e^B + e^-B]/4

= [e^A + e^-A]/2 + 4 [e^B + e^-B]/2


LHS == RHS
Reply 2
just as i thought woo! cracker of a question... elpaw beat me to it...