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## Turan graphs

Prove the following :

Let \(G\) be a simple graph with \(n\) vertices. If \(G\) has more than \(\lfloor \frac{n^2}{4} \rfloor\) edges, then \(G\) contains a triangle.

Let \(G\) be a simple graph with \(n\) vertices, such that \(G\) contains no \(K_{r+1}\). Prove that the number of edges in \(G\) is at most

\(\left(\frac{r-1}{r}\right)\frac{n^2}{2}\)