可设x＝4cosθ,y＝2√3sinθ.
∴Z＝x-2y
＝4cosθ-4√3sinθ
＝8cos(θ+π/3).
∴cos(θ+π/3)＝1时,Z|max＝8;
cos(θ+π/3)＝-1时,Z|min＝-8.