The fourth term of a G.P. is 27, and the 7th term is 729, find the G.P.
Tn = arn-1
a =a, r =?, Tn = 27 n=4
a =a, r =?, Tn = 729 n=7
∴ 27 = a.r4-1
⇒ 27 =a.r3…(1)
∴ 729 = a.r7-1
⇒ 729 = a.r6…(2)
Divide (2) by (1) we get
⇒
⇒ r3 = 27
⇒ r = 3
Substituting r in 1 we get
a = 1
∴ GP = 1,3,9…