Question

cos la 2a 120 grade + sin la 2a 60 grade

Answer 1

cos120°=cos(90°+30°)=-cos30°=-$\frac{ \sqrt{3} }{2}$,   sin60°=$\frac{ \sqrt{3} }{2}$, deci suma este = $(\frac{- \sqrt{3} }{2})^2+( \frac{ \sqrt{3} }{2})^2= \frac{3}{4}+ \frac{3}{4}= \frac{3}{2}$