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Question
Which term of the AP 21, 18, 15, … is zero?
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Solution
In the given AP, first term, a = 21and common difference, d = (18-21) = - 3
Let’s its nth term be 0.
Then, Tn = 0
⇒ a +(n-1) d=0
⇒ 21 + (n-1) × (-3) =0
⇒ 24 - 3n = 0
⇒ 3n = 24
⇒ n= 8
Hence, the 8th term of the given AP is 0.
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