[tex] sin^{2}_a + cos^{2}_a = 1 \\ \\ sin_a = \frac{ \sqrt{3}}{2} \Rightarrow sin^{2}_a = \frac{3}{4} \\ \\ cos^{2}_a =1 - sin^{2}_a = 1 - \frac{3}{4} = \frac{4}{4} - \frac{3}{4} = \frac{1}{4} \\ \\ Unghiul \ a \ este \ ascutit \ \rightarrow a \ apartine \ C_1 ( 0; \frac{ \pi}{2} ) \\ \\ cos_a = \sqrt{ \frac{1}{4}} = \frac{1}{2} [/tex]
