Question: closed form solution

I am having issues with Maple 2016 computing closed form solutions using the sum command. For example, sum((-1)^n, n = 1 .. infinity) evaluates to -1/2 in the help topic, however, when I run the command in a maple document, this result is not obtained. It instead returns sum((-1)^n, n = 1 .. infinity). Likewise, sum( a*r^k, k = 0..infinity) doesn't evaluate to -a/(r-1). How can I get Maple to determine closed form solutions for power series?

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