题目

已知正实数a，b满足，则的取值范围为_________． 答案：【答案】【解析】先根据正实数a，b满足找到a，b的关系及a，b的范围，然后把通换元法转化为函数求值域．由得，∴，且．∵，∴，∴∴．则，令则在上递减，（因为），∴．令，则，∴=在上单增，∴．故答案为：(6,9)．2. Stumpy and his wife Martha went to the state      (义卖会) every year.