Q55 of 202 Page 9

The sum of the first n terms of an A.P. is 3n2 + 6n. Find the nth term of this A.P.

Let ‘a’ be the first term and ‘d’ be the common difference

Sn= 3n2 + 6n


Firsdt term, a, S1 = 3(1)2 + 6(1)


= 3 + 6 = 9


S2 = 3(2)2 + 6(2)


a + a + d = 12 + 12


9 + 9 + d = 24


18 + d = 24


d = 6


Therefore, an = a + (n – 1) d


= 9 + (n – 1) 6


= 6n + 3


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