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Math Help - tough one

  1. #1
    rakan00
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    tough one

    hello please help me understand this question...thanxThe complement graph G of a simple graph G has the same vertices as G, and two vertices are adjacent in G if and only if they are not adjacent in G.If G is a simple graph with 15 edges and G has 13 edges, how many vertices does G have?
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  2. #2
    MHF Contributor

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    The graph with its complement forms a complete graph, a graph with 28 edges. Now, solve the following combination: if Combin(n,2)=28 then n=?
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  3. #3
    rakan00
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    so (n)(2)=28 how to solce thisis it n*28/2please help
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  4. #4
    MHF Contributor

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    Dont you know about combinations?
    If not how are you expected to work such a problem?

    The combination of n vertices taken 2 at a time is [n(n-1)/2].
    That number is 28. Solve for n.
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  5. #5
    rakan00
    Guest
    n^2 - 1/ 2=28>>> n^2= 7*8 +1n=7.54is that right and how would you solve it with combination.... please show me the method to do thatthanx much
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