Question

Which term of the AP: 21, 18, 15, ........is -81 ?​

Answer 1

Answer:

let -81 is the nth term of the given AP

here a=21

d=18-21=-3

we know that, tn=a+(n-1) d

this implies, -81=21+(n-1) ×-3

-81=21-3n+3

-81=24-3n

3n=24+81

3n=105

n=105/3

n= 35

therefore, -81 is the 35th term of the given AP.

hope it helps you mate.