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Let Sn denote the sum of first n terms o...

Let `S_n` denote the sum of first n terms of a G.P. whose first term and common ratio are a and r respectively. On the basis of above information answer the following question: `S_1+S_2+S_2+..+S_n=` (A) `(na)/(1-r)-(ar(1-^n))/((1-r)^20` (B) `(na)/(1-r)-(ar(1+^n))/((1+r)^20` (C) `(na)/(1-r)-(a(1-^n))/((1-r)^20` (D) none of these

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