Posted by haifeng on 2025-06-02 21:04:25 last update 2025-06-02 21:06:40 | Answers (1) | 收藏
用 $\cos x$ 表示 $\cos 2x$, $\cos 4x$, $\cos 6x$.
\[ \cos 2x=2\cos^2 x-1, \]
\[ \cos 4x=8\cos^4 x-8\cos^2 x+1, \]
\[ \cos 6x=32\cos^6 x-48\cos^4 x+18\cos^2 x-1. \]
