Question

4. If nth term of an A.P. is ( 2n + 1 ), what is the sum of its first three terms ?

Answer 1

here is your answer........

Answer 2

Given that nth term of an AP is 2n + 1.

(i) Substitute n = 1:

⇒ a₁ = 2(1) + 1

        = 3.

(ii) Substitute n = 2:

⇒ a₂ = 2(2) + 1

        = 5

(iii) Substitute n = 3:

⇒ a₃ = 2(3) + 1

        = 7

Here, First term a = 3.

Common difference d = 5 - 3 = 2

Sum of first n term of an AP = (n/2)[2a + (n - 1) * d]

⇒ S₃ = (3/2)[2(3) + (3 - 1) * 2]

         = (3/2)[6 + 4]

         = (3/2)[10]

         = 15.

Therefore, Sum of first three terms = 15.

Hope it helps!