Gilbert

The first series is the sum of infinite terms of a geometric sequence whose first term is a = e^(-z) and ratio also r = e^(-z) this sequence is a decreasing sequence

and as you probably know the sum of infinite terms os such a sequence is given by the formula S =a/1-r .

Apply this formula and you will have the first summ in front of you...good luck with the other...don't expect every thing from us...do some homework as well.

MINOAS