f(x)=2sin(π-x)cosx
=2sinxcosx
=sin2x
T=2π/2=π
答：最小正周期为π
x∈[-π/6,π/2]
2x∈[-π/3],π]
f(x)=sin2x
f(x)max=f(π/2)=1
答：最大值为1