۱) $\tan \theta = \frac{\sin \theta}{\cos \theta}, \cos \theta \neq 0$

۲) $\cot \theta = \frac{\cos \theta}{\sin \theta}, \sin \theta \neq 0$

۳) $\tan \theta = \frac{1}{\cot \theta}$ یا $\tan \theta . \cot \theta = 1$

۴) $\sin^2 \theta + \cos^2 \theta = 1 \Rightarrow \begin{cases} \sin^2 \theta = 1 - \cos^2 \theta \\ \cos^2 \theta = 1 - \sin^2 \theta \end{cases} \Rightarrow \begin{cases} \sin \theta = \pm \sqrt{1 - \cos^2 \theta} \\ \cos \theta = \pm \sqrt{1 - \sin^2 \theta} \end{cases}$

۵) $1 + \tan^2 \theta = \frac{1}{\cos^2 \theta}$

۶) $1 + \cot^2 \theta = \frac{1}{\sin^2 \theta}$