Question

求解题，谢谢！

Answer 1

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

A∩B = { x| -1/2≤x<2 }
CrA = { x| x< -1/2 or x>3 }
(CrA)U B = { -2<x< -1/2 }

(2)
(CrA)∩B =B
=> B is subset of CrA

case 1: B =Φ
=> a>0

case 2: B≠Φ , ie a≤0
CrA = { x| x< -1/2 or x>3 }
B={x| x^2+a < 0 } = { x| -√a<x<√a }
B is subset of CrA
case 2: 舍去

(CrA)∩B =B
=> a>0