Q44 of 84 Page 5

The sum of first n terms of an AP is 3n2+4n. Find the 25th term of this AP. (CBSE 2013)

Sum of first n terms of an AP is given by-


Sn = 3n2+4n


∴ S25 = 3(25)2+4(25) = 3×625+100 = 1975


and,S24 = 3(24)2+4(24) = 3×576+96 = 1824


Thus, 25th term of AP = S25- S24 = 1975 - 1824 =151

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