(i) 9, 15, 21, 27,…………
(ii) 11, 6, 1, – 4,……..

Solution: 

The given progression is 9, 15, 21, 27,…………
We can see that, 15 – 9 = 21 – 15 = 27 – 21 = 6 (Constant)
Thus, we can say that each term differs from its preceding term by 6. So, the given progression is an Arithmetic Progression.
here, the first term = 9
and the common difference =6
So, the next term of the AP will be

= 27 + 6 = 33

(ii) The given progression is 11, 6, 1, – 4,……..
We can see that, 6 – 11 = 1 – 6 = –4 – 1 = –5 (Constant)
Thus, we can say that each term differs from its preceding term by 6. So, the given progression is an Arithmetic Progression.
here, the first-term = 11
and the common difference = –5
Then, the next term of the Ap will be:

= -4 + (-5) = -9