题目

不等式的解集是 ． 答案：【答案】【解析】试题根据题意，由于不等式，则根据正切函数的周期为，那么可知一个周期内满足的解集为，那么在整个定义域内为，故答案为。 Mr．Li has some trouble sleeping, so dinking a glass of milk before going to bed every night is his common ________． [　　] A．practice B．knowledge C．experience D．duty