x=8/3a+8/3,y=-2/3a+10/3
a<1/5
(2)分类讨论
a≤-11/8
-8a-11+10a+1=2a-10
-11/8<a<-1/10
8a+11+10a+1=18a+12
a≥-1/10
8a+11-10a-1=10-2a