(Q18).Which of the following forms an AP? If they form an AP, then write the next two terms?

(i) 1, 1, 1, 2, 2, 2, 3, 3, 3, . . .

a2 – a1 = – =

a3 – a2 = – =

a4 – a3 = – =

Here, a2 – a1 = a3 – a2 ≠ a4 – a3.

So, the given list of numbers does not form an AP.