问题
选择题
如果ac＜0，那么下面不等式：①
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答案
∵ac＜0
∴a，c异号
∴①
＜0成立a c
又∵a与a3同号，c与c3同号
∴a3与c异号，a与c3异号
∴④a3c＜0；⑤ac3＜0
当a＜0时②a2c＜0不成立；当c＜0时③ac2＜0不成立．正确的是：①④⑤，故选C．
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如果ac＜0，那么下面不等式：①
|
∵ac＜0
∴a，c异号
∴①
＜0成立a c
又∵a与a3同号，c与c3同号
∴a3与c异号，a与c3异号
∴④a3c＜0；⑤ac3＜0
当a＜0时②a2c＜0不成立；当c＜0时③ac2＜0不成立．正确的是：①④⑤，故选C．
Jack is a clerk of a bookstore. Here is the note from his boss, Ben. Jack has to decide what books to order according to the following note and the descriptions of the books. Hi Jack, You must hand in the order list of books to me by the first working day of every month. The rules for choosing books are: For textbooks: ● August is coming. We must choose all textbooks, without thinking of other rules. For books which are not textbooks: ● If more than five copies of books were sold last month, we choose them. But if there are five copies or more in stock (现货), we do not make an order. ● If the wholesale (批发) prices of the books are higher than $75, we do not choose them. And we do not order anything whose retail (零售) price is higher than $100. Ben The descriptions of the books
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