T
thanhthinh_mx
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
![](https://blog.hocmai.vn/wp-content/uploads/2017/07/hot.gif)
1) cosx+cos3x+2cos5x=0
2)sinx+2cotx=3...................................................................................
2)sinx+2cotx=3...................................................................................