集合{6，-9,12，-15，18，-21，24}的真子集列举
1、集合A为7个元素，列举该集合的全部子集。
元素最少时，即1个元素也没有，此时有子集A1=∅；
元素最多时，即有7个元素，此时有子集A2=A,即：
A2={6,-9,12,-15,18,-21,24}。
2、含1个元素的子集，此时有7个子集，具体列举如下：
A3={6}，A4={-9}，A5={12};
A6={-15}，A7={18}，A8={-21};
A9={24}；
3、有2个元素的子集情况，此时个数为C(7,2)=21个，
A10={6,-9}，A11={6,12}，A12={6,-15};
A13={6,18}，A14={6,-21}，A15={6,24};
A16={-9,12}，A17={-9,-15}，A18={-9,18};
A19={-9,-21}，A20={-9,24}，A21={12,-15};
A22={12,18}，A23={12,-21}，A24={12,24};
A25={-15,18}，A26={-15,-21}，A27={-15,24};
A28={18,-21}，A29={18,24}，A30={-21,24};
4、有3个元素的子集情况，此时个数为C(7,3)=35个，列举如下：
A31={6,-9,12}，A32={6,-9,-15}，A33={6,-9,18};
A34={6,-9,-21}，A35={6,-9,24}，A36={6,12,-15};
A37={6,12,18}，A38={6,12,-21}，A39={6,12,24};
A40={6,-15,18}，A41={6,-15,-21}，A42={6,-15,24};
A43={6,18,-21}，A44={6,18,24}，A45={6,-21,24};
A46={-9,12,-15}，A47={-9,12,18}，A48={-9,12,-21};
5、 A49={-9,12,24}，A50={-9,-15,18}，A51={-9,-15,-21};
A52={-9,-15,24}，A53={-9,18,-21}，A54={-9,18,24};
A55={-9,-21,24}，A56={12,-15,18}，A57={12,-15,-21};
A58={12,-15,24}，A59={12,18,-21}，A60={12,18,24};
A61={12,-21,24}，A62={-15,18,-21}，A63={-15,18,24};
A64={-15,-21,24}, A65={18,-21,24};
6、有4个元素的子集情况，此时个数为C(7,4)=C(7,3)=35个，列举如下：
A66={6,-9,12,-15}，A67={6,-9,12,18};
A68={6,-9,12,-21}, A69={6,-9,12,24};
A70={6,-9,-15,18}，A71={6,-9,-15,-21};
A72={6,-9,-15,24}，A73={6,-9,18,-21};
7、A74={6,-9,18,24}, A75={6,-9,-21,24};
A76={6,12,-15,18}, A77={6,12,-15,-21};
A78={6,12,-15,24}, A79={6,12,18,-21};
A80={6,12,18,24}, A81={6,12,-21,24};
8、A82={6,-15,18,-21}, A83={6,-15,18,24};
A84={6,-15,-21,24}, A85={6,18,-21,24};
A86={-9,12,-15,18}, A87={-9,12,-15,-21};
A88={-9,12,-15,24}, A89={-9,12,18,-21};
9、A90={-9,12,18,24}, A91={-9,12,-21,24};
A92={-9,-15,18,-21}, A93={-9,-15,18,24};
A94={-9,-15,-21,24}, A95={-9,18,-21,24};
A96={12,-15,18,-21}, A97={12,-15,18,24};
A98={12,-15,-21,24}, A99={12,18,-21,24};
A100={-15,18,-21,24};
10、有5个元素的子集情况，此时个数为C(7,5)=C(7,2)=21个，列举如下：
A101={6,-9,12,-15,18}, A102={6,-9,12,-15,-21};
A103={6,-9,12,-15,24}, A104={6,-9,12,18,-21};
A105={6,-9,12,18,24}, A106={6,-9,12,-21,24};
11、A107={6,-9,-15,18,-21}, A108={6,-9,-15,18,24};
A109={6,-9,-15,18,24}, A110={6,-9,18,-21,24};
A111={6,12,-15,18,-21}, A112={6,12,-15,18,24};
12、A113={6,12,-15,-21,24}, A114={6,12,18,-21,24};
A115={6,-15,18,-21,24}, A116={-9,12,-15,18,-21};
A117={-9,12,-15,18,24}, A118={-9,12,-15,-21,24};
A119={-9,12,18,-21,24}, A120={-9,-15,18,-21,24};
A121={12,-15,18,-21,24};
13、此时个数为C(7,6)=C(7,1)=7个，列举如下：
A122={6,-9,12,-15,18,-21};
A123={6,-9,12,-15,18,24};
A124={6,-9,12,-15,-21,24};
A125={6,-9,12,18,-21,24};
A126={6,-9,-15,18,-21,24};
A127={6,12,-15,18,-21,24};
A128={-9,12,-15,18,-21,24}。
