Transcript 12.1 Surface Areas of Prisms

12.3 Surface Areas of Circular
Solids
OBJECTIVE
AFTER STUDYING THIS SECTION,
YOU WILL BE ABLE TO FIND THE
SURFACE AREAS OF CIRCULAR
SOLIDS
Cylinders
 A cylinder resembles a prism in having two congruent
parallel bases. The bases are circles.
 If we look at the net of a cylinder,
we can see two circles and a
rectangle.
 The circumference of the circle is
the length of the rectangle and
the height is the width.
Theorem
 The lateral area of a cylinder is equal to the product
of the height and the circumference of the base
L. A.cyl  Ch  2 rh
 where C is the circumference of the base, h is the
height of the cylinder, and r is the radius of the base.
Definition
 The total area of a cylinder is the sum of the cylinder’s
lateral area and the areas of the two bases.
T . A.cyl  L. A.  2 Abase
Cone
 A cone resembles a pyramid but its base is a circle.
The slant height and the lateral edge are the same in
a cone.
Slant height (italicized l)
height
radius
Theorem
 The lateral area of a cone is equal to one-half the
product of the slant height and the circumference of
the base
L. A.cone
1
 Cl   rl
2
 where C is the circumference of the base, l is the slant
height, and r is the radius of the base.
Definition
 The total area of a cone is the sum of the lateral area
and the area of the base.
T . A.cone  L. A.  Abase
Sphere
 A sphere is a special figure with a special surface-area
formula. (A sphere has no lateral edges and no lateral
area).
Postulate
T . A.sphere  4 r
 where r is the sphere’s radius
2
Example 1
 Find the total area of the figure
6
5
Example 2
 Find the total area of the figure
6
5
Example 3
 Find the total area of the figure
5
Summary
 Explain in your own words how to find the surface
area of a cylinder?
 Homework: worksheet