Question

Which term of the AP 21, 18, 15, ... is zero?

Answer 1

In the given AP, first term, a = 21and common difference, d = (18-21) = - 3

Let’s its n^th   term be 0.

Then, T_n = 0

⇒ a +(n-1) d=0

⇒ 21 + (n-1) × (-3) =0

⇒ 24 - 3n = 0

⇒ 3n = 24

⇒ n= 8 

 Hence, the 8^th  term of the given AP is 0.