Q2 of 47 Page 1

If the nth term of the A.P. –1, 4, 9, 14, ...... is 129, find the value of n.

Given A.P. Series: –1, 4, 9, 14, ......

Since the series is an A.P. series hence between every consecutive terms there is a common difference (d)


We know that the nth term in an A.P. series is given by


tn = a + (n–1)d


where


tn : Represents the nth term of an A.P.


a : Represents the first term of the A.P. series


d : Represents the common difference


n : Represents the position of nth term of the A.P.


So according to the problem:


129 = -1 + (n-1) × 5


⇒ 130 = (n-1) × 5


⇒ n-1 = 26


Answer: The value of n = 27


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