Question

. 9th term of arithmetic sequence is99 , and 99th term is 9. Find its common difference

Answer 1

Answer:

Let a and d be the first term and the common difference respectively of an ap.

(a.n)=a+(n-1)d

Given 9th term=99

   a+8d=99--------------(1)

Given 99th term=9

   a+98d=9-------------(2)

Subtract 1 from 2

a+98d-(a+8d)=9-99

a+98d-a-8d=-90

90d=-90

d=-90/90

d=-1