## Extremal graphs

Let \(G\) be a simple undirected graph with \(2n\) nodes and no triangles (i.e., cycles of length \(3\)). Prove that \(\mathcal G\) has at most \(n^2\) edges.

Let \(G\) be a simple undirected graph with \(2n\) nodes and no triangles (i.e., cycles of length \(3\)). Prove that \(\mathcal G\) has at most \(n^2\) edges.