0<=2x+1/2<=2 ----- -1/4<=x<=3/40<=2x-1/2<=2----- 1/4<=x<=5/4取交集 1/4<=x<=3/4
0≤2x+1/2≤2,解得-1/4≤x≤3/40≤2x-1/2≤2,解得1/4≤x≤5/4[-1/4,3/4]∩[1/4,5/4]=[1/4,3/4]
