Question

The 7th term of an AP is –1 and its 16th term is 17. The nth term of the AP is ______.

विकल्प

• (3n + 8)

• (4n – 7)

• (15 – 2n)

• (2n – 15)

Answer 1

The 7th term of an AP is –1 and its 16th term is 17. The nth term of the AP is (2n – 15).

Explanation:

T₇ = –1 ⇒ a + 6d = –1.  ...(i)

T₁₆ = 17 ⇒ a + 15d = 17.   ...(ii)

On solving (i) and (ii), we get a = –13 and d = 2.

∴ T_n = a + (n – 1)d

= –13 + (n – 1) × 2

= (2n – 15)