COS23XCOS2X - COS2X = 0. 5/  SIN 0X221SIN 71    X

4/ - GIAI DE THI LUONG GIAC
GIAI DE THI LUONG GIAC
4/ cos

2

3xcos2x - cos

2

x = 0. 5/

 

sin 0x21sin 71    x