Question

The sum of n terms of an AP is 3n² + 5n. The number of term which equals 164 is ______.

Options

• 13

• 21

• 27

• None of these

Answer 1

The sum of n terms of an AP is 3n² + 5n. The number of term which equals 164 is 27.

Explanation:

S_n = 3n² + 5n

T_n = S_n – S_n–1

= 3n² + 5n – [3(n – 1)² + 5(n – 1)]

= 164 given

⇒ 6n + 2 = 164

⇒ n = 27