Question

How many terms of the G.P. 3, 9, 27, 81, .......... must be taken to make the sum 3279 ??????

Answer 1

Hello dear,

$3279 = \frac{a(1 - {r}^{n} ) }{(1 - r)} \\ = > 3279 = \frac{3(1 - {3}^{n} )}{(1 - 3)} \\ = > - \frac{6558}{3} =( 1 - {3}^{n} ) \\ = > {3}^{n} = \frac{3 + 6558}{3} \\ = > \frac{6561}{3} = {3}^{n} \\ = > 2187 = {3}^{n} \\ = > {3}^{7} = {3}^{n} \\ = > n = 7$


a=3. ,r=9/3=3

Answer 2

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