Binomial theorem for expansion of the constant term, who can give me an example to see

Binomial theorem for expansion of the constant term, who can give me an example to see

This is too simple, for example, (ax-b) ^ n for constant term, the constant term is (- 1) ^ n × C (n) 1 × (2) ^ n = n × (- 1) ^ n × (b) ^ n

If (3a2-2a13) & nbsp; n expansion contains constant term, then the minimum value of positive integer n is ()
A. 4B. 5C. 6D. 8

The general term of the expansion is tr + 1 = CrN (3a2) n − R (− 2a13) r = crn3n − R · (− 2) ra2n − 53r, let 2n − 53r = 0, then n = 53r, ∵ R ∈ n *, when r = 3, the minimum value of positive integer n is 5, so the answer is 5