四十六角形
cos  2 π 46 = cos  π 23 = cos  ( π − 22 π 23 ) = − cos  22 π 23 = − λ 1 σ 2 + λ 2 σ 4 + λ 3 σ 6 + λ 4 σ 8 + λ 5 σ 10 + λ 6 σ + λ 7 σ 3 + λ 8 σ 5 + λ 9 σ 7 + λ 10 σ 9 − 1 22 {\displaystyle {\begin{aligned}\cos {\frac {2\pi }{46}}=&\cos {\frac {\pi }{23}}=\cos \left(\pi -{\frac {22\pi }{23}}\right)=-\cos {\frac {22\pi }{23}}\\=&-{\frac {\lambda _{1}\sigma ^{2}+\lambda _{2}\sigma ^{4}+\lambda _{3}\sigma ^{6}+\lambda _{4}\sigma ^{8}+\lambda _{5}\sigma ^{10}+\lambda _{6}\sigma +\lambda _{7}\sigma ^{3}+\lambda _{8}\sigma ^{5}+\lambda _{9}\sigma ^{7}+\lambda _{10}\sigma ^{9}-1}{22}}\end{aligned}}}