#4: What is tricky about this is coordinating the vertices and edges of the triangle

Correct ways to split up the triangle	V, F and E for correct ways	Incorrect ways to split up the triangle	What's wrong
	V=3, E=3, F=2 3-3+2=2		Edges have to go between vertices, so there has to be at least one vertex.
	V=1, E=1, F=2 1-1+2=2		Edges go between vertices. If there isn't a vertex, the edge just keeps going--an edge doesn't split into two edges without a vertex.

5. Again, it's the tricky triangles that cause the problems

Correct ways to split up the shape	V, F and E for correct ways	Incorrect ways to split up the shape	What's wrong
	V=2, E=3, F=3 2-3+3=2		Edges go between vertices. If there isn't a vertex, the edge just keeps going--an edge doesn't split into two edges without a vertex.
	V=6, E=7, F=3 6-7+3=2

6. Surprise, surprise, it's tricky triangles that cause problems again (maybe I should have made up some problems with tricky squares)

Correct ways to split up the shape	V, F and E for correct ways	Incorrect ways to split up the shape	What's wrong
	V=2, E=3, F=3 2-3+3=2		Edges go between vertices. If there isn't a vertex, the edge just keeps going--an edge doesn't split into two edges without a vertex.
	V=4, E=5, F=3 4-5+3=2