Question Number 176086 by amin96 last updated on 11/Sep/22
Commented by mahdipoor last updated on 11/Sep/22
$$?=\frac{\mathrm{1}}{\mathrm{2}{cosa}}\approx\mathrm{1}.\mathrm{4142} \\ $$$${a}={tan}^{−\mathrm{1}} \left(\frac{{sin}\frac{\mathrm{720}}{\mathrm{7}}+{sin}\frac{\mathrm{360}}{\mathrm{7}}−\mathrm{4}{sin}\left(\frac{\mathrm{90}}{\mathrm{7}}\right){sin}\left(\frac{\mathrm{900}}{\mathrm{7}}\right)}{{cos}\frac{\mathrm{360}}{\mathrm{7}}+{cos}\frac{\mathrm{720}}{\mathrm{7}}}\right) \\ $$$$ \\ $$