倍角公式：2sinα•cosα=sin2α∴f(x)=sin2x + sin[2•(x + π/4)]=sin2x + sin(2x + π/2)诱导公式：=sin2x + cos2x=√2•[(√2/2)sin2x + (√2/2)cos2x]=√2sin(2x + π/4)
