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

Advertisement Remove all ads

#### Solution

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.

Concept: Sum of First n Terms of an AP

Is there an error in this question or solution?

#### APPEARS IN

Advertisement Remove all ads