题目

阅读理解。        Xiaofan, a smart boy from Shenzhen, used to have difficulty in getting up on time, and his alarm clock was of no use at all. It made him very upset. One day, he had a good idea.        Xiaofan went to a shop and bought a tape. Back home, he started to record what he wanted. After that, he took out a tool box and connected his tape player with the new tape to his alarm clock. A special alarm clock was born. At a certain time in the morning, the tape player would play soft music with a low and sweet voice of a young girl, “Wake up, please.” Five min已知恒成立，则实数的取值范围是        .