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…


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