Q58 of 202 Page 9

The sum of first n terms of an A.P. is 5n – n2. Find the nth term of this A.P.

Sn = 5n – n2

First term, a = 5(1) – (1)2


= 5 – 1 = 4


S2 = 5(2) – (2)2


a + (a + d) = 10 – 4


4 + 4 + d = 6


d = -2


Now, the nth term, an = a + (n - 1) d


= 4 + (n – 1) (-2)


= 4 + 2 – 2n = 6 – 2n


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