Wow thanks i just figured out that identity ( if thats what its called) that i had seen before but have never used. I get that part now.
But now if i divide through by n^2 i get
which is still wrong..if the answer is 1/3 then should i be dividing through by n rather than n^2? Well i just tried that but then i get
This doesn't make sense, as i need a 3 in the denominator so i guess one of these terms, i guess the first , should evaluate to 2, and the second to 1. Sorry now i am just taking stabs in the dark