Question Number 92000 by student work last updated on 04/May/20
$$\mathrm{proof}\:\mathrm{0}!!=\mathrm{1} \\ $$
Answered by $@ty@m123 last updated on 04/May/20
$${n}!={n}.\left({n}−\mathrm{1}\right)! \\ $$$$\Rightarrow\left({n}−\mathrm{1}\right)!=\frac{{n}!}{{n}} \\ $$$${Put}\:{n}=\mathrm{1} \\ $$$$\Rightarrow\mathrm{0}!=\mathrm{1} \\ $$