y=(5x-1)／(4x+2) =(5x+5/2-7/2)/(4x+2) =(5x+5/2)/(4x+2)-7/[2(4x+2)] =5/4-7/(8x+4) 因为7/(8x+4)不等于0, y=5/4-7/(8x+4)不等于5/4 所以 y=（5x-1）／（4x+2）的值域为y不等于5/4
