Question

I was thinking. A square pyramid has 4 triangular faces and a square base. Each triangular face has 3 sides, which are
edges of the pyramid. So there should be 4 times 3, or 12, lateral edges, plus the 4 on the square base—16 edges in all.
But I counted and found only 8 edges. What is wrong with my reasoning?”

Answer 1

you counted each face edge twice, since the triangles touch.