函数f（x）=√3asinxcosx+2cosx的平方-1
f（π/3）=√3asinπ/3cosπ/3+2cosπ/3的平方-1
=3a/4+1/2-1=0
a=2/3
f（x）=2√3/3sinxcosx+2cosx的平方-1
=√3/3sin2x+cos2x
=2√3/3(1/2*sin2x+√3/2cos2x)
=2√3/3sin(2x+π/3)
T=2π/2=π
2kπ-π/2