Find the sum to n terms of the series 3×1^3 + 5×2^2 + 7×3^2+...
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3.1^2+5.2^2+7.3^2+.....
here qe use concept of sigma ,
sigma (2r+1).r^2
=> sigma 2r^3+r^2
=> 2.sigma r^3+sigma r^2
=> 2. {n (n+1)/2}^2+n (n+1)(2n+1)/6
here qe use concept of sigma ,
sigma (2r+1).r^2
=> sigma 2r^3+r^2
=> 2.sigma r^3+sigma r^2
=> 2. {n (n+1)/2}^2+n (n+1)(2n+1)/6
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