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    Question

    Find sum of first n terms: 2 + 6 + 12 + 20 + 30 +

    …
    A n(n-2)(n+1)/3 Correct Answer Incorrect Answer
    B n(n+1)(n+2)/3 Correct Answer Incorrect Answer
    C n(n+1)(n-2)/5 Correct Answer Incorrect Answer
    D n(n-1)(n-2)/3 Correct Answer Incorrect Answer

    Solution

    ATQ,

    Series = n(n+1). Sum = Σn(n+1) = Σn² + Σn = [n(n+1)(2n+1)/6] + [n(n+1)/2] =  n(n+1)(2n+1+3)/6 = n(n+1)(n+2)/3

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