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How Do I Calculate A Polynomial Curve Fit

For Excel 2007 -

I am looking for a function [or method] to calculate a polynomial curve fit. I can do it on a graph with the existing graph and chart tools, but I need to calculate it myself. Does such software exist somewhere in my Excel 2007 package, or can anyone recommend a freeware program? I am hesitant to download an unknown, un-recommended add-in.

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