sin 2 u = 2 sin u cos u {\displaystyle \sin {2u}=2\sin {u}\cos {u}}
cos 2 u = cos 2 u − sin 2 u = 2 cos 2 u − 1 = 1 − 2 sin 2 u {\displaystyle {\begin{aligned}\cos {2u}&=\cos ^{2}{u}-\sin ^{2}{u}\\&=2\cos ^{2}{u}-1\\&=1-2\sin ^{2}{u}\end{aligned}}}
tan 2 u = 2 tan u 1 − tan 2 u {\displaystyle \tan {2u}={\frac {2\tan {u}}{1-\tan ^{2}{u}}}}
此資料改編自原始的 CK-12 書籍，可在 此處 找到。此作品是根據 Creative Commons Attribution-Share Alike 3.0 United States License 授權的
