1.

(1)2+(2)2+(3)2+...+(n-1)2 =?​

Answer»

1² + 2² + 3² + .... + (N - 1)²

Applying the SUMMATION formula

\sf \Sigma n^2 = \frac{n(n + 1)(2n + 1)}{6}

So, for (n - 1) TERMS,

\sf sum = \frac{(n - 1)(n - 1 + 1)(2n - 2 + 1)}{6}

\sf sum = \frac{n(n - 1)(2n - 1)}{6}



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