^2+(a-1)x+a^2=0
判别式=(a-1)^2-4a^2=-3a^2-2a+1=(-3a+1)(a+1)>=0
-1<=a<=1/3
x^2+2ax-2a=0
判别式=(2a)^2+8a=4a^2+8a>=0
a<=-2或者a>=0
两解集取并得 a<=-2或者a>=-1