Question
$\frac{1}{{1!(n - 1)\,!}} + \frac{1}{{3!(n - 3)!}} + \frac{1}{{5!(n - 5)!}} + .... = $
$\frac{{n!}}{{1!(n - 1)!}} + \frac{1}{{3!}}.\frac{{n!}}{{(n - 3)\,!}} + \frac{1}{{5!}}.\frac{{n!}}{{(n - 5)!}} + ....$
$ = {\,^n}{C_1} + {\,^n}{C_3} + {\,^n}{C_5} + .... = {2^{n - 1}}$.
इस प्रकार $\frac{1}{{1!(n - 1)!}} + \frac{1}{{3!(n - 3)!}} + \frac{1}{{5!(n - 5)!}} + ... = \frac{1}{{n!}}{2^{n - 1}}$.
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$\mathrm{f}(\mathrm{x})=\frac{1}{\sqrt{[\mathrm{x}]^2-3[\mathrm{x}]-10}}$, (जहाँ $[\mathrm{x}]$ महत्तम पूर्णांक $\leq \mathrm{x}$ है, का प्रांत है)