A=x|x<-2 or x≥3}, B={x|ax+1<0}
ax+1<0
ax<-1
case 1: a<0
ax<-1
x> -1/a
B含于A
=>
-1/a ≥3
-1≤ 3a
a≥ -1/3
solution for case 1: -1/3≤a<0
case 2: a=0
B=Φ
=>B含于A
solution for case 2: a=0
case 3: a>0
ax<-1
x<-1/a
B含于A
=>
-1/a ≤-2
-1≤-2a
a≤ 1/2
solution for case 3: 0<a≤ 1/2
//
ie
B含于A
case 1 or case 2 or case 3
-1/3≤a<0 or a=0 or 0<a≤ 1/2
-1/3≤a≤1/2