Question

If the n^th term of an AP is (2n +1), then the sum of its first three terms is ______.

Options

• 6n + 3

• 15

• 12

• 21

Answer 1

If the n^th term of an AP is (2n +1), then the sum of its first three terms is 15.

Explanation:-

a₁= 2 × 1 + 1 = 3,

a₂ = 2 × 2 + 1 = 5,

a₃ = 2 × 3 + l = 7

∴ Sum = 3 + 5 + 7 = 15