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

  1. May 26, 2016 #1
    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,

  2. jcsd
  3. May 27, 2016 #2
    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.
  4. May 27, 2016 #3
    Thank you, micromass.
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