=2√3sinxcosx+2cos^2x- 1
=√3sin2x+cos2x
=2sin(2x+π/6)
(1) Minimum period T=2π/2=π
x∈[π/6，π/4]
2x+π/6∈π/2，2π/3
sin(2x+π/6)∈√3/2， 1
F(x)=2sin(2x+π/6) Maximum value =2
Minimum value =√3