- #1

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[tex]

\sum\limits_{k = 0}^N {r^k } = \frac{{1 - r^{N + 1} }}{{1 - r}}

[/tex]

There are other related things I am slightly worried about but I can't remember what they are at the moment so I might post them later. In the mean time, any verification of the above formula that I have quoted would be good thanks.