Question

已知集合a={ x|0<x<a} b={ x|1<x<2} ,若b包含于a,求实数a的取值范围.

Answer 1

A={ x|0<x<a}, B={ x|1<x<2} ,若B包含于A
solution:
A≠Φ
=> a>0 (1)
B包含于A
=> a≥2 (2)
B包含于A
(1) and (2)
a>0 and a≥2
=> a≥2