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

Class 10nth Term of an APAlgebra — Sequences

A9th
B8th
C10th
D7th

Step-by-Step Solution

a = 21, d = - 3. a_{n} = 21 + (n - 1) (- 3) = 24 - 3 n < 0 \Rightarrow 3 n > 24 \Rightarrow n > 8

, so first negative term is the 9th

(a_{9} = 24 - 27 = - 3)

.

Answer: A) 9th

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