分式两边同乘以(x^2+1),整理可得
y*x^2+-x+y-2=0;
当y=0时,x=-2,有解
当y不等于0时,其根的判别式1-4y^2+8y
由题可知,y一定有解,即y*x^2+-x+y-2=0有解,所以判别式1-4y^2+8y>=0恒成立
解得(2-根号5)/2<=y<=(2+根号5)/2