a seemingly easy but really hard question

Q23:

If –4 < x < 7 and –6 < y < 3, which of the following specifies all the possible values of xy?

A.     –42 < xy < 21

B.     –42 < xy < 24

C.     –28 < xy < 18

D.     –24 < xy < 21

E.      –24 < xy < 24

答案是B. 请教NN怎样解这种题? 谢谢.

NN都跑哪儿BBQ去了?

Q23:

If –4 < x < 7 and –6 < y < 3, which of the following specifies all the possible values of xy?B.     –42 < xy < 24

就-4，-6，7，3，这几个数，你算算最大最小的就OK啦

最大=-4*-6=24 最小=7*-6=-42  

谢谢YY