七十角形
2 cos  2 π 70 + ω ⋅ 2 cos  22 π 70 + ω 2 ⋅ 2 cos  38 π 70 = 5 − 47 5 − 15 14 ( 5 + 5 ) + 4 14 ( 5 − 5 ) + 3 3 ( − 7 + 7 5 − 14 ( 5 + 5 ) + 2 14 ( 5 − 5 ) ) i 8 3 2 cos  2 π 70 + ω 2 ⋅ 2 cos  22 π 70 + ω ⋅ 2 cos  38 π 70 = 5 − 47 5 − 15 14 ( 5 + 5 ) + 4 14 ( 5 − 5 ) − 3 3 ( − 7 + 7 5 − 14 ( 5 + 5 ) + 2 14 ( 5 − 5 ) ) i 8 3 {\displaystyle {\begin{aligned}2\cos {\frac {2\pi }{70}}+\omega \cdot 2\cos {\frac {22\pi }{70}}+\omega ^{2}\cdot 2\cos {\frac {38\pi }{70}}=&{\sqrt[{3}]{\tfrac {{5-47{\sqrt {5}}-15{\sqrt {14\left(5+{\sqrt {5}}\right)}}+4{\sqrt {14\left(5-{\sqrt {5}}\right)}}}+3{\sqrt {3}}\left(-7+7{\sqrt {5}}-{\sqrt {14\left(5+{\sqrt {5}}\right)}}+2{\sqrt {14\left(5-{\sqrt {5}}\right)}}\right)i}{8}}}\\2\cos {\frac {2\pi }{70}}+\omega ^{2}\cdot 2\cos {\frac {22\pi }{70}}+\omega \cdot 2\cos {\frac {38\pi }{70}}=&{\sqrt[{3}]{\tfrac {{5-47{\sqrt {5}}-15{\sqrt {14\left(5+{\sqrt {5}}\right)}}+4{\sqrt {14\left(5-{\sqrt {5}}\right)}}}-3{\sqrt {3}}\left(-7+7{\sqrt {5}}-{\sqrt {14\left(5+{\sqrt {5}}\right)}}+2{\sqrt {14\left(5-{\sqrt {5}}\right)}}\right)i}{8}}}\\\end{aligned}}}