Pearson Geometry Common Core, 2011
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Pearson Geometry Common Core, 2011 View details
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Exercise 5 Page 755

Euler's Formula states that the sum of the number of faces and vertices of a polyhedron is two more than the number of its edges.

12

Practice makes perfect
Let's start by drawing the described polyhedron. We are told that it has seven faces — one of the faces is an hexagon and the remaining six are triangles.

The hexagon contributes with six edges. Moreover, there is another extra edge for each of the six vertices of the hexagon. These are the edges that come together to create the triangles. The number of edges of the polyhedron is the sum of these. 6+6=12 edges