A等于{X的2次方-(a+3)X+3a=0}={(x-3)()x-a)=0}={3,a},a≠3或A={3},a=3B={x的二次方-3X+2=0}={(x-1)(x-2)=0,}={1,2},(1).当a=3A∪B={1,2,3},A∩B=φ(2).当a=1A∪B={1,2,3},A∩B={1}(3).当a=2A∪B={1,2,3},A∩B={2}(4)...