Pre-Algebra Demystified

The perimeter of a square is found by using the formula P¼4s, where s is the

length of a side.

EXAMPLE

Find the perimeter of the square shown in Fig. 9-6.

SOLUTION

P¼4s

¼ 4 7 inches

¼28 inches

The perimeter of a circle is called thecircumferenceof a circle. To find the

circumference of a circle, it is necessary to use either the radius (r) or the

diameter (d) of the circle.

The radius of a circle is equal to one-half of its diameter: i.e.,r¼ 21 dord 2.

The diameter of a circle is twice as large as its radius: i.e.,d¼ 2 r.

EXAMPLE

Find the radius of a circle if its diameter is 16 inches.

SOLUTION

r¼

1

2

d

¼

1

2

16 inches

¼8 inches

EXAMPLE

Find the diameter of a circle when its radius is 14 inches.

168 CHAPTER 9 Informal Geometry

Fig. 9-6.