Because that is how a polyhedron is defined.
Because that is how a polyhedron is defined.
Because that is how a polyhedron is defined.
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A polyhedron is defined as a three-dimensional figure composed entirely of flat polygonal faces, which meet at edges and vertices. In contrast, a three-dimensional figure with a curved surface, such as a sphere or cylinder, lacks flat faces and instead has continuous curves. Therefore, the presence of a curved surface disqualifies such figures from being classified as polyhedra.
A polyhedron.
It is so by definition.
A paraboloid.
A polyhedron is a three-dimensional solid with flat faces, straight edges, and sharp corners, while a non-polyhedron does not have these characteristics. Polyhedra are made up of polygons that enclose a single region of space, while non-polyhedra may have curved faces or intersecting edges. In mathematical terms, a polyhedron satisfies Euler's formula (V - E + F = 2), where V is the number of vertices, E is the number of edges, and F is the number of faces, while a non-polyhedron does not.
Cylinder - a solid figure formed by two congruent parallel circles joined by a curved surface.
cube
Sphere
A semicircle