中心对称所以x=4π/3时y=0所以2π/3+φ=kπ+π/2所以φ=kπ-π/6所以k=0|φ|最小=π/6
2x4π/3＋φ=π/2+kπφ=-13π/6+kπ│φ│=π/6
2x4π/3＋φ-2π=0│φ│=2π/3
