Thread: 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?

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=?

so (n)(2)=28 how to solce thisis it n*28/2please help

Don’t 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.

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