# explain why a cylinder is not a polyhedron.?

• Well one definition of a polyhedron is: “A 3-dimensional solid with flat surfaces as faces. A polyhedron need not be convex or bounded.”

A cylinder fails this test because the sides are not flat, but rather are curved.

• Is A Cylinder A Polyhedron

• In classical mathematics, a polyhedron (from Greek πολυεδρον, from poly-, stem of πολυς, “many,” + -edron, form of εδρον, “base”, “seat”, or “face”) is a three-dimensional shape that is made up of a finite number of polygonal faces which are parts of planes; the faces meet in pairs along edges which are straight-line segments, and the edges meet in points called vertices. Cubes, prisms and pyramids are examples of polyhedra.

a cylinder is a quadric surface. There are no polygonal faces which are parts of planes

• I think it might be V=2, E = 1 and F =1 . Imagine that you stretch the cilinder and you obtain a rectangular. ABCD where the vertex A is “identified” with B, the vertex C is “identified with” D, so the side AC is “identified” with BD. So there are 2 vertices, one edge AC and one face ABCD. Anyhow I don’t guarantee the proof( though such procedures are used in algebraic topology). But at wikipedia you finf the formula for Euler characteristic: The Euler characteristic of a closed orientable surface can be calculated from its genus g (the number of tori in a connected sum decomposition of the surface; intuitively, the number of “handles”) as χ = 2 − 2g. Now the cilinder is a orientable surface and its number of “handles” is 0, so X = 2 – 0 = 2 (not surprising) I need to read more algebraic toplogy.

• a polyhedron is a solid formed by plane faces

a cylinder is a round (non-planar) solid

• It doesn’t consist entirely of flat surfaces, for a start.

• it has rounded sides with no corners