Question

Which term of A.P. 21, 18, 15.... is - 81 ?? ​

Answer 1

Answer:

-81 =a+(n-1)d

-81 =21+(n-1)d

- 81=21-3n+3

-81=24-3n

-81-24=-3n

-105=-3n

-105/-3=n

35=n

The 35 th term of AP is - 81

Answer 2

Answer:

Step-by-step explanation:

Solution :-

Given :-

1st Term, a = 21

Difference, d = 18 - 21 = -3

a (n) = -81

To Find :-

nth term

Solution :-

⇒ aₙ = a + (n - 1)d

⇒ -81 = 21 + (n - 1)(-3)

⇒ -81 = 24 - 3n

⇒ -105 = -3n

⇒ n = -105/-3

⇒ n = 35

Hence, the 35th term of the given AP is  -81.