Important Concepts and Formulas
2. If in any polyhedron, the line
segment joining any two points on its surface lie entirely inside or on the
polyhedron, then the polyhedron is called a convex polyhedron.
3. If the faces of a polyhedron are
regular polygons and the same number of faces meet at each vertex, then the
polyhedron is called regular polyhedron.
4. The intersection of two adjacent
faces of a solid is called an edge.
5. A plane surface enclosed by edges is
called a face.
6. A point where three edges meet is
called a vertex.
7. A net of a solid is a plane figure
(2D shape) that can be folded up to form the solid (3D shape).
8. A prism is a polyhedron for which the
top and bottom faces are congruent polygons and all other faces are
parallelograms.
9. A pyramid is a polyhedron whose base
is a polygon and whose lateral faces are triangles having a common vertex.
10. For a polyhedron, if F is the number
of faces, V is the number of vertices and E is the number of edges, then F + V
– E = 2. It is called Euler’s formula.
11. A map scale is usually represented as
a ratio (for example, 1 : r) or as a fraction (for example, 1/r ).