Stim ca
[tex]\sin{2x}=2\sin{x}\cos{x}[/tex] si
[tex]\sin^{2}{x}+\cos^{2}{x}=1[/tex]
Asadar avem urmatoarea relatie
[tex]\frac{2}{\sin{(2x)}}=\frac{2}{2\sin{x}\cos{x}}=\frac{1}{\sin{x}\cos{x}}=\frac{\sin^{2}{x}+\cos^{2}{x}}{\sin{x}\cos{x}}=\frac{\sin^{2}{x}}{\sin{x}\cos{x}}+\frac{\cos^{2}{x}}{\sin{x}\cos{x}}=\frac{\sin{x}}{\cos{x}}+\frac{\cos{x}}{\sin{x}}=tgx+ctgx}[/tex]
