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Grade 12th passAlgebra

Find the sum of 1.2+3.4+5.6+7.8+..................................................................

Profile image of sudhanshu Tripathi
8 Years agoGrade 12th pass
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1 Answer

Profile image of Shailendra Kumar Sharma
8 Years ago
Tr= (2r-1)(2r+2)
Tr = 4r2 +4r-2r-2
Tr= 4r2+2r-2
So Sn = \sum (4r2+2r-2)
Sn= 4{n(n+1)(2n+1)/6} +2 {n(n+1)}/2 -2n
    =2/3{n(n+1)(2n+1)+ n(n+1)-2n