y=(sinx-2)/(cosx+1) ycosx+y=sinx-2 ycosx-sinx=-2-y √[y+(-1)]sin(x+θ)=-2-y √(1+y)sin(x+θ)=-2-y sin(x+θ)=(-2-y)/√(1+y) -1≤sin(x+θ)≤1 -1≤(-2-y)/√(1+y)≤1 y≤-3/4 值域：(-∞,-3/4]