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प्रश्न
Write the sum of the series 2 + 4 + 6 + 8 + ... + 2n.
उत्तर
\[S_n = 2 + 4 + 6 + 8 + . . . + 2n\]
\[= \frac{n}{2}\left[ 4 + \left( n - 1 \right)2 \right]\]
\[ = \frac{n}{2}\left[ 2 + 2n \right]\]
\[ = n\left[ n + 1 \right]\]
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