Q. 154.4( 47 Votes )

Given a G.P. with a = 729 and 7th term 64, determine S7.

Answer :

Given: a = 729 and a7 = 64.


nth term of a G.P is given by arn-1


a7 = ar7-1


64 = 729 × (r)6


r6 =


r6 =


r =


The Sum of terms in G.P. is given by: ( r < 1)



37 – 27 = 2187 – 128 = 2059


S7 = 2059


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