y = 根号2/2(sin3x-cos3x)
= sin3x * 根号2/2 - cos3x * 根号2/2
= sin3xcosπ/4 - cos3xsinπ/4
= sin(3x-π/4)
= sin{3(x-π/12)}
向右平移 π/12个单位后得到y=sin3x