Question

Find the series in A.P whose sum to n terms is n*(n+2)​

Answer 1

3, 5, 7, 9, 11, .........

Explanation:

Given

`S_(n)` = n(n + 2) , then

S₁ = 1(1 + 2) = 1(3) = 3 ⇒ a₁ = 3

S₂ = 2(2 + 2) = 2(4) = 8

S₃ = 3(3 + 2) = 3(5) = 15

Thus

a₂ = S₂ - S₁ = 8 - 3 = 5

a₃ = S₃ - S₂ = 15 - 8 = 7

The first 3 terms are 3, 5, 7

This is an AP with common difference d = 2, then

a₄ = a₃ + 2 = 7 + 2 = 9

a₅ = a₄ + 2 = 9 + 2 = 11

and so on