# why should we use cell phones

## why should we use cell phones

CHAPTER

9

Geometry
9.1 Perimeter
9.2 Area
9.3 Circles
9.4 Volume
9.5 Angles and Triangles

9.6 Square Roots and the Pythagorean Theorem

Slide 2

9.1

Perimeter
OBJECTIVES

a Find the perimeter of a polygon.
b Solve applied problems involving perimeter.

Slide 3

9.1

Perimeter

Perimeter of a Polygon
A polygon is a closed geometric figure with three or
more sides. The perimeter of a polygon is the
distance around it, or the sum of the lengths of its
sides.

Slide 4

9.1

Perimeter

a Find the perimeter of a polygon.
EXAMPLE A Find the perimeter of this polygon.
9m
Solution

5m
4m

Add the lengths of all sides.
8m
Perimeter = 5 m + 4 m + 6 m + 8 m + 9 m
= (5 + 4 + 6 + 8 + 9) m
= 32 m

6m

Slide 5

9.1

Perimeter

Perimeter of a Rectangle
A rectangle is a polygon with four sides and four 90
degree angles.
The perimeter of a rectangle is twice the sum of
the length and the width, or 2 times the length plus
2 times the width.
l
P = 2l + 2w, or P = 2  (l + w).
w
w
l

Slide 6

9.1

Perimeter

a Find the perimeter of a polygon.
EXAMPLE B Find the perimeter of a barn door that is 10
f by 12 f.
Solution
P = 2l + 2w
= 212 f + 210 f
= (212) f + (210) f
= 24 f + 20 f
= 44 f

Slide 7

9.1

Perimeter

Perimeter of a Square
A square is a rectangle in which all sides have the
same length.
The perimeter of a square is four times the length
s
of a side.
P = 4s
s
s
s

Slide 8

9.1

Perimeter

a Find the perimeter of a polygon.
EXAMPLE C Find the perimeter of a square garden with
sides of length 15 feet.
Solution
P = 4s
= 4 ∙ 15 f
= 60 f