1. Binomial Expansion : (a + b)n = nC0an + nC1an-1b + nC2an-2b2 + ...+ nCn-1a.bn-1 + nCnbn
2. General Term of an Expansion : (a + b)n is Tr+1 = nCran-rbr
3. Middle Term of an Expansion : In the expansion (a + b)n, if n is even, then the middle term is the (n/2 + 1)th term. 
                                 If n is odd, then the middle terms are (n + 1)/2 th and [(n + 1)/2 + 1] th terms.