Question

Which term of the AP 21, 18, 15 ...... is -81 ?​

Answer 1

Given AP is 21 ,18,15,...

First term = 21

Common difference = 18-21 = -3

Let an = -81

We know that

an = a+(n-1)d

⇛21+(n-1)(-3) = -81

⇛ 21-3n+3 = -81

⇛24-3n = -81

⇛ 24+81 = 3n

⇛ 105= 3n

⇛ n = 105/3

⇛ n = 35

35th term of the AP is -81.

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