题目

— What time do you usually have your first class?— ______ eight o'clock _____ the morning. A . At, on B . At, in C . On, in D . On, at 答案：B已知函数f（x）=cos2x+3sin2x①求f（x）的最小正周期及其单调区间；②当x取何值时，f（x）取最大值？最大值是多少？③在直角坐标系内，画出f（x）在一个周期内的图象．