Asked by mafo

the first term of arithmetic progression is -8 .and the ratio of the 7th and the 9th term is 5 :8 .find the common difference.
Answered by Reiny
term7 = a+6d = 6d-8
term9 = a+8d = 8d-8

(6d-8)/(8d-8) = 5/8
48d - 64 = 40d - 40
8d = 24
d = 3