M·N=1
√3/2sinx/2＋cos²x/4=1
√3/2sinx/2＋﹙1＋cosx/2﹚/2=1
√3/2sinx/2＋1/2×cosx/2=1/2
sin﹙x/2＋π/6﹚=1/2
cos（2π/3-x）=-cos（π-2π/3＋x）=cos﹙x＋π/3﹚=1-2sin²﹙x/2＋π/6﹚=1/2