Answers

2014-06-26T15:16:11+08:00
Solution:

(1,3,5), (1,3,7), (1,3,9), (1,5,7), (1,5,9), (1,7,9), (3,5,7), (3,7,9), (5,7,9),
(1,3), (1,5), (1,7), (1,9), (3,5), (3,7), (3,9), (5,7), (5,9), (7,9)
(1), (3), (5), (7), (9)

( )


Answer:  ( ) is an empty set.
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