Use GeoGebra to calculate sums, including infinite series. These are a lot of work to compute by hand, but GeoGebra makes it easy. 
     GeoGebra Instruction 1
CAS     under         View     in         Menu.         Sum(<Expression>, <Variable>, <Start Value>, <End Value>).
Type the expression for           in <Expression>. Type        for <Variable>. Insert the start value of          in <Start Value>,         and the end value of        in <End Value>.         
If you want to compute an infinite series, type inf in <End Value> (inf is short         for infinity).