MN长度=gx-fx =根号3cos2x-2sin^2(派/4+x) =根号3cos2x + 1-cos2(x+π/4) =根号3cos2x + sin2x +1 =2sin(2x+π/3)+1最大值 3 当且仅当2x+π/3=2kπ+π/2 k∈z
数形结合把