Mathematics Asked on February 13, 2021
Here is the well known theorem, "For planar graph $G$, if $vgeq3$ then $eleq 3(v-2)$"
I’ve reviewed my discrete mathematics note, suddenly the question crossed my mind.
When we proving the $eleq 3(v-2)$ for planar graph, $G$. We used $d(f) geq 3$.
In my note, it told me the reason why does $d(f) geq 3$ is "each face is bounded by at least three edges, but each edge borders two faces."
When I first saw it, it was clear for me. But the time passed I doubt about that.
Because… Let me suggest the counter example below.
The above graph is planar graph and $v=3, e=2,f=1$. But the $d(f) lt 3$ (I.e. the face is not bounded three edges)
Still I’ve confused what the point did I mistake.
Any help would be appreciated.
Your counterexample is discussed in this answer. Because the edges are boundaries of the same face, in the proof the "boundary of the face" has 4 edges (each edge is counted twice).
Correct answer by angryavian on February 13, 2021
Get help from others!
Recent Questions
Recent Answers
© 2024 TransWikia.com. All rights reserved. Sites we Love: PCI Database, UKBizDB, Menu Kuliner, Sharing RPP