1.y=sin[2(x-π/12)] 左移π/12 可得到y=sin2x
2.√3/3 ≤tanx ≤ √3
kπ+π/6≤x≤kπ+π/3
3.arccosx≤arccos(1-x)
-1≤x≤1,-1≤1-x≤1,x≥1-x
解得：1/2≤x≤1