1/[2x+(1-x^2/x)] = 1/[2x + (1 - x) ] = 1/ (2x + 1 - x) = 1/(x + 1)
不过我觉得这个题目是不是应该是
1/[2x + (1- x^2) / x] = 1/[(1+x^2)/x] = x/(1+x^2) = x + 1/x