Page 100 - Math Course 1 (Book 2)

Polygons

B. Name the polygon by its number of sides. CD = 2 2
Then classify it as convex or concave, regular [3 –(–3)] + [–4 –(–4)]
or irregular.
2
= 6 + 0 2
= 36 or 6

2
DE = [3 –(–3)] + [–4 –1] 2
There are 9 sides, so this is a nonagon. = 0 + (–5) 2
2
A line containing some of the sides will pass
through the interior of the nonagon, so it is = 25 or 5
concave.
2
EA = (–3 – 0) + [1 – 4] 2
Since the polygon is concave, it must be irregular.
2
nonagon, concave, = (–3) + (–3) 2
Answer
irregular = 18 ≈ 4.2

The perimeter of pentagon is
Perimeter and Area on the Coordinate Plane
32
17
Answer ABCDE + + 6 + 5 +
Examples 18 or about 25 units.

Find the perimeter of a pentagon ABCDE with Your Turn!
A(0, 4), B(4, 0), C(3, –4), D(–3, –4), and E(–3, 1).

Identify Polygons

A. Name each polygon by the number of sides.
Then classify it as convex or concave, regular
or irregular.

A. triangle, concave, regular
B. triangle, convex, irregular
C. quadrilateral, convex, regular
D. triangle, convex, regular

Answer
Use the Distance Formula, d = (x –x ) + (y –y ) 2
2
2 1 2 1
to f nd AB, BC, CD, DE, and EA.
B. Name each polygon by the number of sides.
AB = (0 – 4) + (4 – 0) 2 Then classify it as convex or concave, regular
2
or irregular.
= 4 + 4 2 A. quadrilateral, convex, regular
2
B. pentagon, convex, irregular
= 32 ≈ 5.7 C. quadrilateral, convex, irregular
D. quadrilateral, concave, irregular
2
BC = (4 – 3) + [0 –(–4)] 2
Answer
2
= 1 + 4 2
= 17 ≈ 4.1

92