Asked by afsana
S8:S4=97:81 find the common ratio
Answers
Answered by
Reiny
Assuming that S8 means Sum(8), and you are dealing with a geometric sequence .....
( a(r^8 - 1)/(r-1) ) / ( a(r^4 - 1)/(r-1) ) = 97/81
(r^8 - 1)/(r^4 - 1) = 97/81
(r^4 - 1)(r^4 + 1)/(r^4-1) = 97/81
r^4 + 1 = 97/81
r^4 = 16/81
r = ± 2/3
( a(r^8 - 1)/(r-1) ) / ( a(r^4 - 1)/(r-1) ) = 97/81
(r^8 - 1)/(r^4 - 1) = 97/81
(r^4 - 1)(r^4 + 1)/(r^4-1) = 97/81
r^4 + 1 = 97/81
r^4 = 16/81
r = ± 2/3