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Let `S_n`denote the sum of first `n`terms of an A.P. If `S_(2n)=3S_n ,`then find the ratio `S_(3n)//S_ndot`A. 4B. 6C. 8D. 10 |
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Answer» Correct Answer - B Let a be the first term and d be the common difference of the A.P. Then, `S_(2n)=3S_(n)` `rArr" "(2n)/(2){2a+(2n-1)d}=(3n)/(2){2a+(n-1)d}rArr2a=(n+1)d`. `:." "(S_(3)n)/(S_(n))=((3n)/(2)[2a+(3n-1)d])/((n)/(2)[2a+(n-1)d])=(3[(n+1)d+(3n-1)d])/([(n+1)d+(n-1)d])=6` |
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