y=sinx-sin(x+π/4)
=2cos[(x+x+π/4)/2]sin[(x-x-π/4)/2]
=-2sin(π/8)cos(x+π/8)
=-2√[(1-cos(π/4)/2]cos(x+π/8)
=-√(4-√2)cos(x+π/8)
ymax=√(4-√2)
ymin=-√(4-√2)
周期：[2kπ-π/8,2kπ+17π/8)为什么前面是系数是2呢..根据和差化积公式：sinθ-sinφ = 2 cos[(θ+φ)/2]sin[(θ-φ)/2]