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`1.3+2.4+3.5+..........n` पदों तकA. `(n(n+1)(2n+3))/(6)`B. `(n^(2)(n+1)^(2))/(4)`C. `(n(n+1)(2n+1))/(6)`D. इनमे से कोई नहीं |
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Answer» Correct Answer - (iv) `t_(n)=n(n+2)=n^(2)+2n` `:.s_(n)=sumt_(n)=sumn^(2)+2sumn=(n(n+1)(2n+1))/(6)+(2n(n+1))/(2)` `=(n(n+1))/(6)[2n+1+6]=(n(n+1)(2n+7))/(6)` |
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