y=(x^2+1-2)/(x^2+1)=1-((2/(x^2+1))由此可知定义域为{x‖x不等于-1和1}因为x^2+1的最小值为1,无最大值所以2/(x^2+1)的值域为（0,2】所以1-((2/(x^2+1))的值域为【-1,1）所以y=(x^2-1)/(x^2+1)的定义域为{x‖x≠-1且...