Analysis: comprehensive investigation of set and its operation, positional relationship between straight line and circle, discussion of parameter classification, distance formula from point to straight line, positional relationship between two straight lines, solving inequalities and difficult problems. What time? When M≤0, set A is centered on (2,0), and the absolute value is m? Is a circle with a radius, and the set b is divided into two? Between two parallel lines, because? There is no solution at this time; When M≥0? Set a takes (2,0) as the center. And then what? Is a circle with a radius, and the set b is between two parallel lines, so there must be? . because