f(x)=4sinx[(√3/2)sinx＋(1/2)cosx]－1
f(x)=2√3sin²x＋2sinxcosx－1
f(x)=√3(1－cos2x)＋sin2x－1
f(x)=2sin(2x－π/3)＋(√3－1)
最小正周期是2π/2=π
当：x∈[－π/6,π/4]
则：2x－π/3∈[－2π/3,π/6]
sin(2x－π/3)∈[－1,1/2]
f(x)∈[√3－3,√3]