sin ⁡ 2 A = 2 sin ⁡ A cos ⁡ A {\displaystyle \sin 2A=2\sin A\cos A} cos ⁡ 2 A = cos 2 ⁡ A − sin 2 ⁡ A = 1 − 2 sin 2 ⁡ A = 2 cos 2 ⁡ A − 1 {\displaystyle \cos 2A=\cos ^{2}A-\sin ^{2}A=1-2\sin ^{2}A=2\cos ^{2}A-1} tan ⁡ 2 A = 2 tan ⁡ A 1 − tan 2 ⁡ A = 2 cot ⁡ A cot 2 ⁡ A − 1 = 2 cot ⁡ A − tan ⁡ A {\displaystyle \tan 2A={\frac {2\tan A}{1-\tan ^{2}A}}={\frac {2\cot A}{\cot ^{2}A-1}}={\frac {2}{\cot A-\tan A}}}