A complete graph is a graph in which there is one edge between every pair of distinct vertices

(distinct here is used to denote that there can't be an edge from a vertex back to itself). How many

edges are in a complete graph with n vertices and why?

A complete graph is a graph in which there is one edge between every pair of distinct vertices (distinct here is used to denote that there can't be an edge from a vertex back to itself). How many edges are in a complete graph with n vertices and why