Question

Find the sum of 12 terms of an A.P. whose nth term is given by a_n = 3n + 4.

Options

• 262

• 272

• 282

• 292

Answer 1

282

Explanation:-

Here a_n = 3n + 4

∴ a₁ = 7, a₂ - 10, a₃ = 13

∴ a = 7, d = 10 - 7 = 3

∴ S₁₂ = `12/2[2 xx 7 + (12 - 1) xx3]`

= 6[14 + 33]

= 6 × 47

= 282