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# Introduction to Three Dimensional Shapes

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Dimension is a property of shapes which tells whether the shape has the height (or depth).

A three dimensional shape also called as a solid shape is a shape which has 3 measurements length, breadth and height. They look different by observing them from different places and different angles. But where as 2d- shapes have only two measurements length and breadth.

A polyhedron is a 3D-shape whose faces are polygons where as a non-polyhedron contains no polygon shaped faces. Examples of polyhedrons can be cubes, cuboids, pyramids and prisms etc.

Polygonal faces are the regions by which the polyhedron is bounded. For example, the polygonal faces of the cube are the squares.

An edge of a polyhedron is a line segment where any two of its faces meet.

A regular polyhedron is a polyhedron whose faces are congruent to each other. Otherwise it is said to be irregular polyhedron. An example for a regular polyhedron is a cube because it has all congruent faces(squares).

A convex polyhedron is a polyhedron where the line segment joining any two points on it lies completely in it.

A concave polyhedron is a polyhedron in which the plane sections are concave.

A prism is a polyhedron where two of its bases are parallel and the side faces are parallelograms.

A pyramid is a polyhedron where the base is a polygon and the side faces are triangles with a common vertex.

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