Question

which term of AP 2,4,21,18,15----- is first negative term?

Answer 1

The given A.P. : 24,21,18….

a= 24

d= -3

n=?

Let us first find which term will be 0.

Using the formula : an= a+(n-1)d

0=24-(n-1)(-3)

24–3n+3=0

n= 9

So 9th term will be 0. Hence 10 term will be first negative. Again using the same formula where n= 10, we get,

An= 24+9(-3)=-3

Hence first negative term is -3

Answer 2

A1=2
A2=4
A3=21
A4=18
A5=15
Answer is 11th term