Question

which term of the AP 121 , 117 , 113 .. is its first negative term

Answer 1

Given Series is 121, 117, 113...

Here,

First term a = 121.

Common difference d = 117 - 121 = -4.

Let the nth term of the AP be the first negative term.

⇒ an < 0

⇒ a + (n - 1) * d < 0

⇒ 121 + (n - 1) * (-4) < 0

⇒ 121 - 4n + 4 < 0

⇒ 125 - 4n < 0

⇒ 125 < 4n

⇒ n > 125/4

⇒ n = 31.25

⇒ n = 32.

Therefore, 32nd term is the first negative term in the given AP.

Hope it helps!