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 P: 117 The difficulty is that I don't know -how- to isolate the k^2 :( I know very little about using this sigma notation, the only rule I know is that when you have sigma(ak + b) you can rewrite as: sigma(ak) + sigma(b) =(a)sigma(k) + (b)sigma(1) where a and b are constants. for me, the problem is that there is a variable on the other side of the addition--2k that is... Again, I know very little of the rules of sigma notation. Perhaps there is a way to rewrite this? I'm not wanting the answer for the area--rather just a more manageable way for me to put it to limits ;) Or is it already to go??? I had just figured I could "do more" to it. Thanks again!