1.a=52.B{2,3},C{2,-4}由题意的A有解且=空集,则x=39-3a+a^2-19=0,a^2-3a-10=0a=-2或5检验a=5时A∩C≠空集所以a=-23.由题意得x=24-2a+a^2-19=0,a^2-2a-15=0a=-3或5检验a=5时A∩B≠A∩C所以a=-3