Find the two middle terms in the expansion of :

For ,

a=3x, and n=9

As n is odd, there are two middle terms i.e.

I. and II.

General term t_r+1 is given by,

I. The first middle term is

Therefore, for 5^th middle term, r=4

Therefore, the first middle term is

II. The second middle term is

Therefore, for the 6^th middle term, r=5

Therefore, the second middle term is

………