Question

If nth term of AP is (2n+1) then the sum of tis first three terms is?

Answer 1

Given that

an = 2n+1        ...(1)

put n=1 in (1), we get

a₁ = 2(1)+1 = 3

put n=2 in (1), we get

a₂ = 2(2)+1 = 5

put n=3 in (1), we get

a₃ = 2(3)+1 = 7

So a₁, a₂ and a₃ are three terms of an AP.

Hence sum of first three term of an AP is  3+ 5+ 7 = 15