諗極都諗唔到呀..

2sinx = tanx
2sinx = sinx/cosx
2sinx cosx = sinx
2sinx cosx - sinx = 0
sinx (2cosx -1) = 0
sinx = 0 or 2cosx -1 =0
x= 180n or cosx = 1/2
x = 360n +/- 60
n is any integer