The formula 𝑬 = 𝑭 + 𝑽 – 2 works for prisms because they are a type of polyhedron. For a triangular prism, 𝑭 = 5, 𝑽 = 6 and 𝑬 = 9. 5 + 6 – 2 = 9. 𝑭 + 𝑽 – 2 = 𝑬.

A triangular prism has five faces, the two triangles for each end plus three rectangular faces that join them. A hexagonal prism has eight faces, the two hexagons for each end plus six rectangular ...