题目

听材料，回答问题。 （1） What does the man intend to do? A . To encourage the woman. B . To test the woman. C . To praise the woman. （2） Where does the conversation take place? A . On a road. B . In a bus station. C . At a hotel. 答案：A A设0＜θ＜,曲线x2sinθ+y2cosθ=1和x2cosθ-y2sinθ=1有4个不同的交点.(1)求θ的取值范围;(2)证明这4个交点共圆,并求圆半径的取值范围.