Number of faces: F=a+3 Number of vertices: V=2a Number of edges: E=4a-1
V+F-E=2 Replacing V=2a; F=a+3; and E=4a-1 in the formula above: (2a)+(a+3)-(4a-1)=2 Eliminating parentheses: 2a+a+3-4a+1=2 Adding similar terms: (2+1-4)a+(3+1)=2 (-1)a+4=2 Solving for a. Subtracting 4 both sides of the equation: (-1)a+4-4=2-4 (-1)a=-2 Dividing both sides by (-1) (-1)a/(-1)=-2/(-1) a=2
