_____________
This is a geometric series
The first term = 5
The common ratio is -2
The sum of the first five terms is
first term [ 1 - common difference^5] / [ 1 - common difference ]
5 [ 1 - (-2)^5 ] / [ 1 - (-2) ] =
5 [ 1 + 32 ] / [ 3] =
5 { 11] =
55
