2x-7x+3=(2x-1)(x-3)<=01/2<=x<=3A={x|1/2≤x≤3}（1）当a=-4时B={x|x^2+a<0}={x|x^2-4<0}={x|-2≤x≤2}A并B={x|-2≤x≤3}A交B={x|1/2≤x≤2}