Cho cos 2x = \( - \frac{4}{5}\) với \(\frac{\pi }{4} < x < \frac{\pi }{2}\). Tính sin x, cos x, \(\sin \left( {x + \frac{\pi }{3}} \right)\), \(\cos \left( {2x - \frac{\pi }{4}} \right)\).

Cho cos 2x = \( - \frac{4}{5}\) với \(\frac{\pi }{4} < x < \frac{\pi }{2}\).

Tính sin x, cos x, \(\sin \left( {x + \frac{\pi }{3}} \right)\), \(\cos \left( {2x - \frac{\pi }{4}} \right)\).