http://www.youtube.com/watch?v=PCu_BNNI5x4 What is the sum of the infinite sequence 1, -1, 1, -1, 1.....? This is a really interesting puzzle to study - which fits very well when studying geometric series, proof and the history of maths. The two most intuitive answers are either that it has no sum or that it sums to zero. ... Continue Reading →