Question

高一数学。，

Answer 1

如图

追答

Answer 2

A={x| 1/2≤x≤3 }
B={ x| |x|+a<0}
(1)
a=-4
B= { x| |x|<4} = { x| -4<x<4 }
A∩B = { x| 1/2≤x≤3 }
AUB ={ x| -4<x<4 }
(2)
(CrA)∩B =B
=> B is subset of CrA
case 1: B=Φ

B={ x| |x|+a<0} = Φ
=> a≥0
case 2: B≠Φ
ie a<0
B={ x| |x|+a<0} = { x| a<x<-a}
CrA = { x| x<1/2 or x>3 }
B is subset of CrA
=> -a≤1/2 or a≥3 ( a<0 )
=> -a≤1/2
=> a≥-1/2
-----------
(CrA)∩B =B
case 1 or case 2
a≥0 or a≥-1/2
=> a≥-1/2

Answer 3