Find the sum of
Source: NCTM Mathematics Teacher, February 2006
Multiply both sides by
The above expression has terms with the middle term equal
We combine the first term to the last term, the second to the next to last and so on
We end up with seven terms, six terms and the middle term . The six terms cancel the six terms leaving the remaining two terms .
We combine the terms in pairs
We end up with thirteen terms and the remaining term