是x/（ x+1) - 1/(x-1)?要学会加括号,否则谁知道你项算什么
通分得到[x(x-1) - x-1]/(x+1)(x-1)
当x->无穷大时,低次项忽略得到
[x(x-1) - x-1]/(x+1)(x-1) x^2/x^2 =1