Use induction to prove that for a finite set A of cardinality n, there are n(n+1)/2 distinct 2-element subsets of A. ?

Update:

i meant n-1

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  • 1 month ago

    Let's start with a set A that has only two elements.  Then

    n(n+1)/2 = 2*3/2 = 3.

    And hence, your proposition is obviously false.  There is only one 2-element subset of A.

    I think you should've said n(n-1)/2.

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