Question
If S1,S2,S3,....Sn are the sums of infinite geometric series whose first terms are 1, 2, 3,...n and whose ratios are 12,13,14,1(n+1) respectively, then find the value of S21+S22+S23+....+S26
Answer: Option B
:
B
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B
S1=11−12=2
S2=21−13=3
Thus, the respective sums are 2,3,4,5,6,7
Sums of square of these numbers =[n(n+1)(2n+1)6]−1=139.
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