Mathematics · 2021
JEE Main · 24 February 2021, Shift 2 · Q71
If n ≥ 2 is a positive integer, then the sum of the series ^n +1 C_2+2(^2 C_2+^3 C_2+^4 C_2+….+^n C_2) is:
If $\displaystyle \mathrm{n} \geqslant 2$ is a positive integer, then the sum of the series $\displaystyle { }^{\mathrm{n}+1} \mathrm{C}_2+2\left({ }^2 \mathrm{C}_2+{ }^3 \mathrm{C}_2+{ }^4 \mathrm{C}_2+\ldots .+{ }^{\mathrm{n}} \mathrm{C}_2\right)$ is :
Official answer
(2)
$\displaystyle \frac{\mathrm{n}(\mathrm{n}+1)(2 \mathrm{n}+1)}{6}$
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JEE Main 2021 Mathematics question, with the answer from NTA’s final answer key. Where our answers come from.