2倍角の公式

$3$\displaystyle{\sin 2{\alpha}=2\sin {\alpha}\cos {\alpha}}$ ⇒

$3$\displaystyle{\begin{array}{lll} \cos 2{\alpha} & ={ \cos }^{2}{\alpha}- { \sin }^{2}{\alpha} & \vspace{6}\\ & =2{ \cos }^{2}{\alpha}- 1 & \vspace{6}\\ & =1- 2{ \sin }^{2}{\alpha} & \vspace{6}\\ \end{array}}$ ⇒

$3$\displaystyle{\tan 2{\alpha}=\frac{\hspace{2} 2\tan {\alpha} \hspace{2}}{\hspace{2} 1- { \tan }^{2}{\alpha} \hspace{2}}}$ ⇒

[に]
[な行]
[索引トップ]

$3$\displaystyle{\sin 2{\alpha}=2\sin {\alpha}\cos {\alpha}}$	⇒

$3$\displaystyle{\begin{array}{lll} \cos 2{\alpha} & ={ \cos }^{2}{\alpha}- { \sin }^{2}{\alpha} & \vspace{6}\\ & =2{ \cos }^{2}{\alpha}- 1 & \vspace{6}\\ & =1- 2{ \sin }^{2}{\alpha} & \vspace{6}\\ \end{array}}$	⇒

$3$\displaystyle{\tan 2{\alpha}=\frac{\hspace{2} 2\tan {\alpha} \hspace{2}}{\hspace{2} 1- { \tan }^{2}{\alpha} \hspace{2}}}$	⇒