Question 1:

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

Answer:

Given A.P. is 121, 117, 113 …

a = 121

d = 117 − 121 = −4

a_n = 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, a_n < 0

125 − 4n < 0

125 < 4n

n > 125/4

n > 31.25

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

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