The middle term in the expansion of (1+x)2n is:
Middle term
= Tn+1 = 2nCn = 1.2.3.......(2n−1)2nn!xn
= 1.3.5......(2n−1)n!×2n(1.2.3..........n)n!xn
= 1.3.5.........(2n−1)n! 2nxn.