√2/4sin(π/4-x)+√6/4cos(π/4-x)=√2/2*[sin(π/4-x)*1/2+cos*√3/2]=√2/2*sin(π/4-x+π/3)=-√2/2*sin(x-7π/12)递增则sin(x-7π/12)递减2kπ-3π/22kπ-11π/12(2kπ-11π/12，2kπ+π/12)
