x/(x-1)＞a+1;
1+1/(x-1)＞a+1;
1/(x-1)＞a;
x＞1;a<0;无解；
x>1,a≥0;x<1+1/a;
x≤1,a<0;x<1+1/a;
x≤1,a≥0,无解