填空题 $\cos2\alpha = \cos^2\alpha - \underline{\quad}$

填空题 $$\sin(-\alpha) = \underline{\quad}$$，$$\cos(-\alpha) = \underline{\quad}$$

填空题 $$\sin(\alpha + \beta) = \underline{\quad}$$

填空题 $$\cos2\alpha = 1 - 2\underline{\quad}$$

填空题 $$\sin2\alpha = \underline{\quad}$$

填空题 $$\tan\alpha = \underline{\quad}$$（$$\cos\alpha \neq 0$$）

填空题 $$\sin^2\alpha + \underline{\quad} = 1$$

填空题 $$\cos2\alpha = 2\underline{\quad} - 1$$

填空题 $$\cos(\alpha - \beta) = \underline{\quad}$$