Graphs: vertices, edges and degree
Read a graph: find the degree of each vertex, compare the sum of the degrees with the number of edges, and see why some graphs cannot exist.
- إيران: الصف ١٢
- روسيا: الصف ١٠
- فرنسا: الصف ١٢
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الدليل
A graph is some points with some lines (or curves) joining pairs of them. Each point is a vertex and each line an edge. Graphs model things that are related: people and their friendships, towns and their roads.
The degree of a vertex is the number of edges at it. An odd degree makes an odd vertex, an even degree an even vertex. The number of vertices is the order of the graph and the number of edges its size.
Here every graph is simple: at most one edge between two vertices and no edge from a vertex to itself. Vertices are named with letters, as in the Iranian book. Tap vertices to select them; tap again to deselect.