用反表示法求函数y=x-1/x+2(x>= -1)的值域

用反表示法求函数y=(x-1)/(x+2)(x≥-1)的值域
∵y=(x-1)/(x+2)
∴y(x+2)= x-1
故：yx+2y=x-1
故：yx-x=-1-2y
故：x(y-1)= -1-2y
故：x=(-1-2y)/ (y-1)
∵x≥-1
故：(-1-2y)/ (y-1)≥-1
故：(-1-2y)/ (y-1)+1≥0
故：-(y+2)/ (y-1)≥0
故：(y+2)/ (y-1)≤0
故：-2≤y≤1