Question Number 216887 by zetamaths last updated on 23/Feb/25
$$\underset{{k}=\mathrm{1}} {\overset{{n}} {\prod}}{cos}\left(\frac{{x}}{\mathrm{2}^{{k}} }\right)={Pn}\left({x}\right) \\ $$$${evaluate}\:{Pn}\left({x}\right)\:\:{and}\:\:{P}_{{n}} \left({x}^{\mathrm{2}} +\mathrm{1}\right) \\ $$$$ \\ $$$$ \\ $$