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Goniometrische functie

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rechthoekige driehoek A B C a b c α β
$$ \begin{aligned} & \sin\alpha = \frac{a}{c} \ \ \ && \sin\beta = \frac{b}{c} \\ \\ & \cos\alpha = \frac{b}{c} && \cos\beta = \frac{a}{c} \\ \\ & \tan\alpha = \frac{a}{b} && \tan\beta = \frac{b}{a} \\ \\ & \cot\alpha = \frac{b}{a} && \cot\beta = \frac{a}{b} \end{aligned} $$
$$ \begin{aligned} &\sin^2\alpha + \cos^2\alpha = 1 \\ \\ &\tan\alpha \cdot \cot\alpha = 1 \ \Rightarrow \\ \\ &\cot\alpha = \frac{1}{\tan\alpha} \\ \\ &\tan\alpha = \frac{\sin\alpha}{\cos\alpha} \\ \\ &\cot\alpha = \frac{\cos\alpha}{\sin\alpha} \end{aligned} $$
$$ \begin{aligned} &\sin(\alpha + \beta) = \\& = \sin\alpha\cos\beta + \cos\alpha\sin\beta \\ \\ &\sin(\alpha - \beta) = \\& = \sin\alpha\cos\beta - \cos\alpha\sin\beta \\ \\ &\cos(\alpha + \beta) = \\& = \cos\alpha\cos\beta - \sin\alpha\sin\beta \\ \\ &\cos(\alpha - \beta) = \\& = \cos\alpha\cos\beta + \sin\alpha\sin\beta \\ \\ &\tan(\alpha + \beta) = \frac{\tan\alpha + \tan\beta}{1 - \tan\alpha\tan\beta} \\ \\ &\tan(\alpha - \beta) = \frac{\tan\alpha - \tan\beta}{1 + \tan\alpha\tan\beta} \end{aligned} $$
$$ \begin{aligned} &\sin\alpha + \sin\beta = \\& = 2\cdot\sin\frac{\alpha + \beta}{2}\cdot\cos\frac{\alpha - \beta}{2} \\ \\ &\sin\alpha - \sin\beta = \\& = 2\cdot\cos\frac{\alpha + \beta}{2}\cdot\sin\frac{\alpha - \beta}{2} \\ \\ &\cos\alpha + \cos\beta = \\& = 2\cdot\cos\frac{\alpha + \beta}{2}\cdot\cos\frac{\alpha - \beta}{2} \\ \\ &\cos\alpha - \cos\beta = \\& = -2\cdot\sin\frac{\alpha + \beta}{2}\cdot\sin\frac{\alpha - \beta}{2} \end{aligned} $$
$$ \begin{aligned} & \sin 2\alpha = 2\cdot\sin\alpha\cos\alpha \\ \\ & \cos 2\alpha = \cos^2\alpha - \sin^2\alpha \\ \\ & \tan 2\alpha = \frac{2\cdot\tan\alpha}{1 - {\tan}^2\alpha} \end{aligned} $$
$$ \begin{aligned} & \left|\sin\frac{\alpha}{2}\right| = \sqrt{\frac{1-\cos\alpha}{2}} \\ \\ & \left|\cos\frac{\alpha}{2}\right| = \sqrt{\frac{1+\cos\alpha}{2}} \\ \\ & \left|\tan\frac{\alpha}{2}\right| = \sqrt{\frac{1-\cos\alpha}{1+\cos\alpha}} \end{aligned} $$
$$ \begin{aligned} & \sin(-\alpha) = -\sin\alpha \\ \\ & \cos(-\alpha) = \cos\alpha \\ \\ & \tan(-\alpha) = -\tan\alpha \\ \\ & \cot(-\alpha) = -\cot\alpha \end{aligned} $$

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