由y=sinx/(cosx+2),可得ycosx +2y =sinx移项并整理2y=sinx-ycosx=根号(1+y²)·(sinxcosφ-cosxsinφ)=根号(1+y²)·sin(x-φ)【其中,tanφ=y】∴sin(x-φ)=2y/根号(1+y²)由|sin(x-φ)|≤1,得|2y/根号(...