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Which term of the A.P. 121, 117, 113 … is its first negative term? [Hint: Find n for an < 0] - Mathematics

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Which term of the A.P. 121, 117, 113 … is its first negative term? [Hint: Find n for an < 0]

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Solution

Given A.P. is 121, 117, 113 …

a = 121

d = 117 − 121 = −4

an = a + (n − 1) d

= 121 + (n − 1) (−4)

= 121 − 4n + 4

= 125 − 4n

We have to find the first negative term of this A.P.

Therefore an < 0

125 - 4n < 0

125 < 4n

`n > 125/4`

n > 31.25

Therefore, 32nd term will be the first negative term of this A.P.

Concept: Sum of First n Terms of an AP
  Is there an error in this question or solution?

APPEARS IN

RD Sharma Class 10 Maths
Chapter 5 Arithmetic Progression
Exercise 5.4 | Q 2.5 | Page 24
NCERT Class 10 Maths
Chapter 5 Arithmetic Progressions
Exercise 5.4 | Q 1 | Page 115
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