Hi, I'm trying to figure out my TI-89. So I want to estimate the 40th partial sum of this series: Sum(40) of (-1^(k+1))/k^4, starting at k=1. My major problem is that I want to use 'k's or 'n's, not 'x's. Is there a difference? I haven't asked my Calc teacher about this yet, but I know that 'k's and 'n's deal with integers while 'x's encompass the real numbers. When I do the sum with 'x', I get a a number -1.08232 but the book shows .094703. I hate the way that all these manuals show n and k, and presume you can input those variables -- but I haven't seen an 'n' or 'k' variable, and when I use the capital letters it doesn't work.