A planar graph is a graph that can be drawn in a plane without any two edges intersecting.
a. Show that neither of the graphs in Figure 9.87 is planar.
b. Show that in a planar graph, there must exist some vertex which is connected to no more than five nodes.
c. Show that in a planar graph, |E| ‰¤ 3|V| ˆ’ 6.