Тригонометрические тождества
\sin^2\alpha+\cos^2\alpha=1
\tg\alpha =\frac{\sin\alpha}{\cos\alpha}\ \ \ \ \ \ \ \ \ \ \ctg\alpha =\frac{\cos\alpha}{\sin\alpha}
\tg\alpha \cdot \ctg\alpha = 1
|\cos \alpha |=\sqrt{1-\sin^2\alpha}\ \ \ \ \ \ \ \ \ \ |\sin \alpha |=\sqrt{1-\cos^2\alpha}
\tg\alpha = \frac{1}{\ctg\alpha}\ \ \ \ \ \ \ \ \ \ \ \ctg\alpha = \frac{1}{\tg\alpha}
1+\tg^2\alpha =\frac{1}{\cos^2\alpha}=sec^2\alpha
1+\ctg^2\alpha =\frac{1}{\sin^2\alpha}=cosec^2\alpha