关于实数x的不等式|x-(a+1)^2/2|<=(a-1)^2/2与x^2-3(a+1)x+2(3a+1)<=0

来源:百度知道 编辑:UC知道 时间:2024/06/05 02:58:41
(其中a属于R)的解集依次为A.B求使A是B的子集的a的取值范围
求详解!

由|x-(a+1)^2/2|<=(a-1)^2/2可得
解集A=< x!2a<=x<=a2+1 >
由x^2-3(a+1)x+2(3a+1)<=0可得
解集B=< x!3a+1<=x<=2 >当且仅当a<=1/3时成立
或B=< x!2<=x<=3a+1 >当且仅当a>=1/3时成立
因为A是B的子集,所以
当a<=1/3时,B=< x!3a+1<=x<=2 >
满足 ( 3a+1<=2a
< 解得a=-1
( a2+1<=2
当a>=1/3时,B=< x!2<=x<=3a+1 >
满足 ( 2<=2a
< 解得1<=a<=3
( a2+1<=3a+1
综上所得a的取值范围是a=-1或1<=a<=3