Question

which term of arithmetic progression: 21,18,15,..... is -81​

Answer 1

Step-by-step explanation:

let -81 be n term of ap

-81=a+(n-1)d

-81=21+(n-1)(-3)

-81-21=-3n+3

-102-3=-3n

-3n=-105

3n=105

n=35

so -81 is 35th term of this ap