– $\sin2\alpha$, $\cos2\alpha$ hám $\text{tg}2\alpha$ funkciyaları arqalı ańlatıwǵa múmkinshilik beretuǵın formulalar: $$\begin{array}{ll} 1) &\sin 2\alpha=2\sin\alpha \cos2\alpha; \\ 2) &\cos2\alpha=\cos^2\alpha-\sin^2\alpha; \\ 3) &\text{tg}2\alpha=\dfrac{2 \text{tg}\alpha}{1-\text{tg}^2\alpha}. \end{array}$$. Bul formulalardan $1-\cos2\alpha=2\sin^2\alpha$, $1+\cos2\alpha=2\cos^2\alpha$ formulaları keltirilip shıǵarıladı.