Page 255 - Start Up Mathematics_8 (Non CCE)

In a triangular prism, there are: C¢
(i) 6 vertices and 9 edges
O
(ii) 2 triangular bases A¢ B¢
(iii) 3 lateral faces

A triangular prism whose lateral edges are perpendicular to its bases is called Axis
a right triangular prism. The lateral faces of a right prism are bounded by C
rectangles (Fig. 16.14).
O¢
A B
Fig. 16.14

D¢ C¢
(b) Rectangular Prism (Fig. 16.15): It is also called a cuboid or rectangular O¢
solid. It has: A¢ B¢
(i) 8 vertices and 12 edges
(ii) 2 rectangular bases Axis
(iii) 4 lateral faces
D C
O
A B
Fig. 16.15

(c) Pentagonal Prism (Fig. 16.16): It has: D¢
(i) 10 vertices and 15 edges E¢ C¢
(ii) 2 pentagons as bases O¢
(iii) 5 lateral faces A¢ Axis B¢
Similarly, if the number of sides in the base of the prism are six, it is D
called a hexagonal prism and so on. If the bases of a quadrilateral prism E C
are parallelograms, it is called a parallelepiped. O
A B
Fig. 16.16
Pyramid
A pyramid is a polyhedron whose base is a polygon and whose side faces are triangles having a common
vertex. Let’s define some terms associated with a pyramid.
Apex: The common vertex of the triangular faces of a pyramid (point Apex V
V in Fig. 16.17) is called the apex of the pyramid.
Lateral edge
Height: The length of the perpendicular from the apex to the base
of a pyramid (VP in Fig. 16.17) is called the height of the pyramid. Height Lateral face

Axis: The straight line joining the apex to the central point of the base Axis
(VO in Fig. 16.17) is called axis of the pyramid. E D

Lateral Edges: The edges through the apex of a pyramid are called its A P O
lateral edges. B C
Fig. 16.17: Oblique pyramid
Lateral Faces: The faces other than the base of a pyramid are called its
lateral faces.

If the base of a pyramid is a polygon of n sides then the pyramid has n triangular lateral faces and 2n edges.

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