Hi all. I have been asked to sum this series:

1+4x+7x^2+10x^3+...+(3N-2)x^

{N-1}
and also asked what the sum is to infinity when |x|< 1

I have all of the formulae (dodgy spelling

) for summing a series and sum to infinity but this one has me stumped; mainly because at the back of the text book the given anser is:

[3/(1-x)^2]-[2/(1-x)]

I just don't know how to get this answer. It's caused a bit of a mental block for me and his becoming quite annoying! Any help on working through to get this answer would be really helpful and much appreciated. Thanks in advance!