Simplification question

*To*: mathgroup at smc.vnet.net*Subject*: [mg110366] Simplification question*From*: Yaroslav Bulatov <yaroslavvb at gmail.com>*Date*: Tue, 15 Jun 2010 02:30:39 -0400 (EDT)

I'd like to verify that the following expression is true for a,b real. It seems to hold numerically. 1/2 Log[(Exp[a + b] + Exp[-a - b])/(Exp[-a + b] + Exp[a - b])] == ArcTanh[Tanh[a] Tanh[b]] I tried Reduce and combinations of TrigToExp/Simplify with no luck, any suggestions?