Pre-Algebra Demystified

The perimeter of a triangle is found by adding the lengths of the three sides:

P¼aþbþc.

EXAMPLE

Find the perimeter of the triangle shown in Fig. 9-4.

SOLUTION

P¼aþbþc

¼6 inches + 6 inches + 4 inches

¼16 inches

The perimeter of a rectangle can be found by using the formula P¼2lþ2w,

where l is the length and w is the width.

EXAMPLE

Find the perimeter of the rectangle shown in Fig. 9-5.

SOLUTION

P¼2lþ2w

¼ 2 10 inchesþ 2 2 inches

¼ 20 þ 4

¼24 inches

CHAPTER 9 Informal Geometry 167

Fig. 9-4.

Fig. 9-5.