Q. 475.0( 3 Votes )

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



Answer :


a = 729

7th term = 64

∴ a7 = ar6, where r is the common ratio.

729r6 = 64

r6 = 64/729

r6 = (2/3)6

r = 2/3 < 1

S7 =
      =

     =

     =

    =

    =

    = 2059

∴ S7 = 2059

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