由已知得 y(x^2+1)=2x^2-1 ,
yx^2-2x^2= -1-y ,
因此 x^2=(-1-y)/(y-2) ,
由 x^2>=0 得 (-1-y)/(y-2)>=0 ,
即 (y+1)/(y-2)<=0 ,
所以 -1<=y<2 ,
即函数值域为｛y | -1≤y<2｝.