回復 69# leo790124 的帖子
\( |z^{20}| = |z^{20} -1 | =1 \) 可得 \( z^{20} = \frac12 \pm \frac{\sqrt{3}}2i \), \( z^{20} -1 = -\frac12 \pm \frac{\sqrt{3}}2i \)
\( z^8 = \frac1{z^{20} -1} = -\frac12 \mp \frac{\sqrt{3}}2i\),而 \( z^4 = z^{8\cdot3 -20} = \frac12 \mp \frac{\sqrt{3}}2i \)
(以上為兩組 ++-- 和 --++ )
由 \( z^4 \) 之值,解得 8 個 \( z \) 值...
(每次寫,過程都不一樣XD)