数据弱......模拟AC的人多了，它就变成了模拟题......
by Carls @ 2017-07-26 11:20:33
不是我说这道题明明是入门难度好不好
by LMB_001 @ 2017-09-02 20:23:27
\cos 2\theta & = & \cos^2 \theta - \sin^2 \theta \\
& = & 2 \cos^2 \theta - 1.
by bdflyao @ 2017-11-02 20:17:19
$$
\cos 2\theta & = & \cos^2 \theta - \sin^2 \theta \\
& = & 2 \cos^2 \theta - 1.
$$
by bdflyao @ 2017-11-02 20:17:32
\cos 2\theta & = & \cos^2 \theta - \sin^2 \theta \\
& = & 2 \cos^2 \theta - 1.
by bdflyao @ 2017-11-02 20:17:41