本经验通过列举方法,介绍七个元素{9,12,15,18,21,24,27}集合的所有子集。
主要方法与步骤
1
集合{9,12,15,18,21,24,27}的子集中,元素最小的没有元素的集合,即为空集;本题{9,12,15,18,21,24,27}中,元素最多的集合就是这个集合的本身,即为7个元素的集合。
2
{9,12,15,18,21,24,27}有1个元素的子集情况:
此时个数为C(7,1)=7个,列举如下:
A3={9},A4={12},A5={15};
A6={18},A7={21},A8={24};
A9={27};
3
{9,12,15,18,21,24,27}两个元素子集,就是从7个元素中每次只取2一个元素构成的集合,则共有21个。计算公式为:C(7,2)=7*6/2=21个。
4
{9,12,15,18,21,24,27}3个元素子集,从7个元素中每次只取3一个元素构成的集合,则共有35个。计算公式为:C(7,3)=7*6*5/6=35个。
5
{9,12,15,18,21,24,27}4个元素子集,就是从7个元素中每次只取4一个元素构成的集合,则共有35个。计算公式为:C(7,4)=C(7,3)=7*6*5/6=35个。
6
A82={9,18,21,24}, A83={9,18,21,27};
A84={9,18,24,27}, A85={9,21,24,27};
A86={12,15,18,21}, A87={12,15,18,24};
A88={12,15,18,27}, A89={12,15,21,24};
A90={12,15,21,27}, A91={12,15,24,27};
A92={12,18,21,24}, A93={12,18,21,27};
A94={12,18,24,27}, A95={12,21,24,27};
A96={15,18,21,24}, A97={15,18,21,27};
A98={15,18,24,27}, A99={15,21,24,27};
A100={18,21,24,27};
7
{9,12,15,18,21,24,27}7个元素中每次取5一个元素构成的集合,则共有21个。计算公式为:C(7,5)=C(7,2)=7*6/2=21个。
A101={9,12,15,18,21}, A102={9,12,15,18,24};
A103={9,12,15,18,27}, A104={9,12,15,21,24};
A105={9,12,15,21,27}, A106={9,12,15,24,27};
A107={9,12,18,21,24}, A108={9,12,18,21,27};
A109={9,12,18,21,27}, A110={9,12,21,24,27};
8
{9,12,15,18,21,24,27},7个元素中每次取6一个元素构成的集合,则共有7个。计算公式为:C(7,6)=C(7,1)=7个。
END注意事项
集合与元素
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