sin(x)、cos(x)周期为2π,tan(x)周期为π；sin(3πx)、cos(3πx)周期为2/3(3πx取值在0到2π之间时,x取值在0到2/3,故其周期为2/3,余下同理),tan(3πx)周期为1/3；sin(2x)、cos(2x)周期为π,tan(2x)周期为π/2.