Write the coefficient of the middle term in the expansion of (1+x)2n.
(1+x)2n
Here k = 2n, which is even number.
So, (2n2+1)(n+1)th term is the middle term.
Coefficient of (r+1)th term in the binomial expansion of (1+x)k is kCr
Coefficient of (n+1)th term in the binomial expansion of (1+x)2n is 2nCn