No of edges*2 = Sum of degrees of vertices

then how No of edges*2 = degree* region...

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What does degree of a region mean...?

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If

fis any face, then the degree off(denoted by degf) is the number of edges encountered in a walk around the boundary of the facef

No. edges = no. of region*(deg/2) (since each edge is part of exactly 2 regions in a planar graph and hence contributes 2 to the sum of degrees)

We have Euler's formula for planar graph

$n - e + f = 2$, where $n$ is the no. of vertices, $e$ is the no. of edges and $f$ is the no. of faces (regions in planar representation)

And we have $2e = 6f = 6 \times 35 = 210 \\ \implies e = 105$.

Now, $n = 2 + 105 - 35 = 72$.

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http://www.personal.kent.edu/~rmuhamma/GraphTheory/MyGraphTheory/planarity.htm

see this resource it might help

see this resource it might help

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Someone plz answer this also

https://gateoverflow.in/4649/when-is-complete-bipartite-graph-regular?show=4649#q4649

https://gateoverflow.in/4649/when-is-complete-bipartite-graph-regular?show=4649#q4649

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