Question Number 127787 by bemath last updated on 02/Jan/21
$$\:\mathrm{csc}^{\mathrm{2}} \left(\frac{\pi}{\mathrm{7}}\right)+\mathrm{csc}^{\mathrm{2}} \left(\frac{\mathrm{2}\pi}{\mathrm{7}}\right)+\mathrm{csc}^{\mathrm{2}} \left(\frac{\mathrm{3}\pi}{\mathrm{7}}\right)\:=?\: \\ $$