Q. 54.6( 9 Votes )

If the nth term of an AP is (2n + 1), then the sum of its first three terms is
A. 6n + 3

B. 15

C. 12

D. 21

Answer :

Given: nth term = 2n + 1

an = 2n + 1

Put n= 1, a1 = 3

Put n= 2, a2 = 5

Put n= 3, a3 = 7

Now, sum of first three terms = 3 + 5 + 7 = 15

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