Question Number 140166 by mathdanisur last updated on 04/May/21
$$\frac{\mathrm{7}−\mathrm{8}\sqrt{\mathrm{7}}{cos}\left(\frac{{arcsin}\left(\frac{\mathrm{3}\sqrt{\mathrm{21}}}{\mathrm{14}}\right)+\mathrm{4}\pi}{\mathrm{3}}\right)}{\mathrm{3}}\:+\:\mathrm{8}{cos}\left(\frac{\mathrm{4}\pi}{\mathrm{7}}\right)=\mathrm{1} \\ $$