（ax+2)／(x+1)≥2
(ax+2)/(x+1)-2≥0
(ax+2-2x-2)/(x+1)≥0
(a-2)x/(x+1)≥0
1.
a-2=0,即a=2时
x∈R,x≠-1
2.
a-2＞0,即a＞2时
x/(x+1)≥0
x≥0或x＜-1
3.
a-2＜0,即a＜2时
x/(x+1)≤0
-1＜x≤0