Q. 94.3( 3 Votes )

The common ratio of a G.P. is 3, and the last term is 486. If the sum of these terms be 728, find the first term.

Answer :

Given: Common Ratio = 3


Sum of GP = 728


Sum of GP for n terms =


Last term say it be n


Tn = arn - 1


486 = a3n - 1



1458 = a.3n …(1)




1456 = a.3n - a…(2)


Subtracting 1 from 2 we get


1458 - 1456 = a.3n - a.3n + a


a = 2.


The first term is 2.


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