Question

find 9th term of Ap -21,-17,-13​

Answer 1

Answer:

We have t

1 =7,t 2 =13,t 3 =19,t 4 =25...

The common difference d=t

2 −t 1=13−7=6

First term a=7,t

15 =?

We know thatt n=a+(n−1)t 15 =7+(15−1)×6

∴ t 15=7+14×6

∴ t 15 =7+84

∴t 15=91

∴ t 15 =91

∴ The fifteenth term of the A.P is 91.