la-3l≥0,(b+1)^2≥0,la-3l+(b+1)^2=0
a-3=0,b+1=0
a=3,b=-1
(a-2b-m)/2-(a-b+m)/2=1
(3+2-m)/2-(3+1+m)/2=1
(5-m)/2-(4+m)/2=1
[(5-m)-(4+m)]/2=1
1-2m=2
m=-1/2