00:01
Hello everyone, in this video for subdivision we have to prove that g and g complement cannot both be planar.
00:09
So we can use the euler's formula which states that for any planar graph with v vertices, e edges and f faces the following equation holds that is v minus e plus f is equal to 2.
00:21
For the complement of the graph g with v vertices and e edges we have v dash is equal to v and e dash is equal to v2 minus e.
00:34
F dash is equal to v2 minus e dash minus v dash which is equal to v2 then substituting the e dash so minus v2 plus e minus v so which is equal to e minus v plus 1 so this is f.
00:53
Substituting these values into euler's formula for g complement so it gives v minus v2 plus e minus v plus 1 is equal to 2.
01:06
Simplifying we get e is equal to v2 minus 1.
01:12
So this is e, this is f and this is for the graph g complement ok.
01:21
So now, now suppose that the both g and g complement are planar then by euler's formula we have v minus e plus f is equal to 2 which is v minus v2 minus 1 this is e then plus f is equal to 2.
01:44
So f is equal to we get v2 minus v plus 3.
01:51
So now simplifying for g complement we have v minus e dash plus f dash is equal to 2 then v minus of v2 minus e plus f dash is e minus v plus 1 is equal to 2 then f dash is equal to v2 minus e plus 1 ok...