Please expand the following at z=0 with steps, if possible: [e^z + e^-z] / 2
Many thanks.
ez = 1 + z + z2/2! + z3 /3! + z4/4! + ...
e-z = 1 - z + z2/2 - z3/3! + z4/4! - ...
So (ez + e-z)/2 = 1 + z2/2! + z4/4! + ...
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Thank you very much, Alan.