Find the middle term(s) of an A.P. 9, 15, 21, 27,…,183.

Solution :

In order to find the middle term of the sequence, first we have to know how many terms are in the given sequence.

n = [(l - a)d] + 1

a = 9, d = 15 - 9 ==> 6 and l = 183

n = [(183 - 9)/6] + 1

n = (174 / 6) + 1

n = 29 + 1 = 30

n = 30(even)

middle terms are (n/2)th term and [(n/2) + 1]th term