Mathematics
Which term of the A.P. 27, 24, 21, 18, …… is the first negative term ?
10th
11th
12th
9th
AP GP
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Answer
Let nth term of the A.P. be the first negative term.
Given,
A.P. = 27, 24, 21, 18, ……
First term (a) = 27 and common difference (d) = 24 - 27 = -3.
By formula,
an = a + (n - 1)d
Since, nth term is less than zero.
∴ a + (n - 1)d < 0
⇒ 27 + (n - 1)(-3) < 0
⇒ 27 - 3n + 3 < 0
⇒ 3n > 30
⇒ n >
⇒ n > 10.
So, n = 11.
Hence, Option 2 is the correct option.
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