Question

If the n^th term of an A.P. is (2n + 1), then the sum, of its first three terms is
(a) 6n + 3
(b) 15
(c) 12
(d) 21

Answer 1

First term(n = 1) = 2(1) + 1 = 3

Second term(n = 2) = 2(2) + 1 = 5

Third term(n = 3) = 2(3) + 1 = 7

Sum of first three terms = 3 + 5 + 7 = 15

Hence, the correct answer is option (b).