Question

Find the sum of first 16 terms of the A.P. whose n^th term is given by an = 5n – 3.

Answer 1

Given, n^th term of A.P. is a_n = 5n – 3

∴ a₁ = 5(1) – 3 = 2

And a₂ = 5(2) – 3 = 7

∴ Common difference, d = 7 – 2 = 5

∴ Sum of n terms of A.P., S_n = `n/2[2a + (n - 1)d]`

∴ S₁₆ = `16/2 [2(2) + (16 - 1)5]`

= 8(4 + 75)

= 8 × 79

= 632