Download Surface area of Pyramids and cones 12-3

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12-3
Pyramids

A pyramid is a polyhedron in which one
face (the base) can be any polygon and
the other faces (the lateral faces) are
triangles that meet at a common vertex
(called the vertex of the pyramid)
Pyramid Parts
The altitude of a pyramid is the
perpendicular segment from the vertex
(also called apex) to the plane of the
base.
 The length of the altitude is the height
(h) of the pyramid.

Pyramid Parts Cont.
A regular pyramid is a pyramid whose
base is a regular polygon.
 The lateral faces are congruent
isosceles triangles.
 The slant height (l) is the length of the
altitude of a lateral face of the pyramid.

Vertex or apex
Lateral Area
The lateral area is the sum of the areas
of the congruent lateral faces.
 Let’s work it out.

l
base
9090
Lateral
s
Face
Lateral Areas of Regular
Pyramids

The lateral area of a regular pyramid is
half the product of the perimeter of the
base and the slant height.
L.A. = ½ pl
Surface area of a Regular
Pyramid

The surface area of a regular pyramid is
the sum of the lateral area and the area
of the base (B).
S.A. = L.A. + B = ½ pl + B
Cones
A cone is like a pyramid but its base is a circle.
 In a right cone the altitude is a perpendicular
segment from the vertex to the center of the
base.
 The height (h) is the length of the altitude.
 The slant height (l) is the distance from the

vertex to a point on the edge of the base
Right cone
l
Lateral Area of a Right Cone

The lateral area of a right cone is half
the product of the circumference of the
base and the slant height
L.A. = ½ (2πr)l = πrl
Surface Area of a Right Cone

The surface area of a right cone is the
sum of the lateral area and the area of
the base.
S.A. = L.A. + B = πrl +πr2
Joke time

What do you get when you cross
geometry and McDonald’s?

A plane cheeseburger
Joke time

Why was the obtuse angle upset?

Because he was never right.
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