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Question
Which term in the A.P. 60, 56, 52, 48, 44, 40, ...... is the first negative term?
Solution
Given A.P. is 60, 56, 52, 48, 44, 40, ...
Here, a = 60, d = 56 – 60 = – 4
Let nth term of the A.P. be the first negative term.
Then an < 0
We know, an = a + (n – 1)d
⇒ 0 > 60 + (n – 1)(– 4)
0 > 60 – 4n + 4
0 > 64 – 4n
4n > 64
n > 16
Hence, 17th term will be the first negative term.
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