|2x-1|+|x+2|≥a²+½a+2|2x-1|+|x+2|=|2x+4-5|+|x+2|>=5/25/2≥a²+½a+2a²+½a-1/2<=02a平方+a-1<=0(2a-1)(a+1)<=0-1<=a<=1/2