回複：請適當陳述歸納法,直接法,對應法.

直接法:a1,a2,...an
1 empt set,c(n,0)
c(n,1)sets only one element
...
c(n,m)sets m lements
...
c(n,n)set n elements.
So,we have c(n,0)+....+c(n,n)=(1+1)^n=2^n
對應法:If the subset has ai let it to 1,don't has to 0.
WE have 1 to 1 subset to f1f2...fn. fi is 1 or 0.
empty set to 00.....0,.......{a1a2....an} to 11...1.
So,we have 2^n by binary.
歸納法is trival,...miss...

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• 謝津京！ -皆兄弟也- ♂ (0 bytes) () 07/19/2010 postreply 18:27:40