Question Number 64173 by Eminem last updated on 14/Jul/19
$${show}\:{tbat}\:\underset{{k}=\mathrm{1}} {\overset{{n}} {\prod}}\left(\mathrm{1}−\frac{{sin}^{\mathrm{2}} \left(\frac{\theta}{\mathrm{2}{n}}\right)}{{sin}^{\mathrm{2}} \left(\frac{\mathrm{2}{k}−\mathrm{1}}{\mathrm{4}}\pi\right)}\right)={cos}\left(\theta\right) \\ $$
Commented by Prithwish sen last updated on 15/Jul/19
$$\mathrm{Is}'\mathrm{nt}\:\mathrm{it}\:\mathrm{cos}^{\mathrm{n}} \left(\frac{\theta}{\mathrm{n}}\right)\:? \\ $$