Which term is independent of x, in the expansion of (x−13x2)9?
(x−13x2)9
Let (r+1)th term be the independent of x in the given expression Tr+1=9Cr(x)9−r(−13x2)r
=9Cr(−13)r(x)9−r−2r=9Cr(−13)r(x)9−3r
This is term is independent of x if
9−3r=0⇒r=3
So, (3+1)th i.e. 4th term is independent of x.