f(X)=cos(√3x+φ)-√3sin(√3x+φ)
=2[(1/2)cos(√3x+φ)-(√3/2)sin(√3x+φ)] tanπ/3=√3
=2[cosπ/3cos(√3x+φ)-sinπ/3sin(√3x+φ)]
=2cos(π/3+√3x+φ)