[tex]cos30 = \frac{ \sqrt{3} }{2} \\ 120= \frac{120*\pi}{180} = \frac{2\pi}{3} \\ sin\frac{2\pi}{3}= +sin \frac{\pi}{3} = \frac{ \sqrt{3} }{2} \\ \\ \Rightarrow cos30 - sin120 = \frac{ \sqrt{3} }{2} -\frac{ \sqrt{3} }{2} =0[/tex]
2pi/3 face parte din cadranul 2, in care sinusul este pozitiv.
