If there is a term containing x2rin(x+1x2)n−3, then :
n-2r is a positive integral multiple of 3
n-2r is even
n-2r is odd
n = 2r
Tp+1=n−3Cpxn−3−px−2p
∴ 2r = n-3-3p p+1 = (n−2r)3
(p+1) is an integer (n-2r) is a positive integral multiple of 3.