Euler's Theorem

Let be a connected planar graph with and . Let be the number of faces determined by the planar embedding¹. Then we conclude that

Imporant: Euler’s Theorem can be only used for proving some graphs are non-planar. Cannot be used to prove a graph is planar.

Corollary 1 §

Let be a planar graph with components. Then in any planar embedding of the number of regions equals:

Corollary 2 §

Let is a planar graph with . Then

Corollary 3 §

Let is a planar bipartite graph with , then

Footnotes §

1. If the graph isn’t presented in its planar embedding, the theorem doesn’t hold. ↩