I Euler's Formula for planar graphs - 1 or 2 ?

1. May 26, 2016

DaTario

Hi All,
Regarding the Euler's formula Vertices - Edges + Faces = constant, for planar graphs what is the most frequent number? 1 or 2?

I understand that it is 2 when the outer region is included in the count.

Best wishes,

DaTario

2. May 27, 2016

micromass

You can use either formula as long as you make it clear whether you include the outer region or not. I have most usually seen $2$ however.

3. May 27, 2016

DaTario

Thank you, micromass.

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