In the binomial expression, we have (a+b)n=nC0an+nC1an−1b+nC2an−2b2+…+nCnbn.....(i)
The coefficients nC0,nC1,nC2,….,nCn are known as binomial or combinatorial coefficients.
Putting a=b=1 in (i), we get nC0+nC1+nC2+…+nCn=2n
Thus, the sum of all binomial coefficients is equal to 2n.
Again , putting a=1 and b=−1 in Eq. (i), we get nC0+nC2+nC4+…=nC1+nC3+nC5+…
Thus, the sum of all the odd binomial coefficients is equal to the sum of all the even binomial coefficients and each is equal to 22n=2n−1. ⇒nC0+nC2+nC4+…=nC1+nC3+nC5+…=2n−1