三角函数周期是有公式的,y=Asin(ωx+σ)和y=Acos(ωx+σ)周期都是T=2π/ω
y=tan(ωx+σ)周期是T=π/ω
（1）T=2π/ω=2π/(1/2)=4π
（2）T=2π/ω=2π/1=2π
（3）T=2π/ω=2π/(2/3)=3π