Basic Mathematics for College Students

Chapter 9 Summary and Review 817

7 x − 46°

B

C

A

D

2 x + 9°

5 x − 33°

H

I

E G

F

3 x + 13°

25. In the figure below,.
    a. Find x.
    b. Find the measure of each angle that is labeled.

ABDC

24. In the figure below,.
    a. Find x.
    b. Find the measure of each angle that is labeled.

l 1 l 2

4 x − 10°

3 x + 50°

l 2

l 1

26. In the figure below,.
    a. Find x.
    b. Find the measure of each angle that is labeled.

EFHI

SECTION 9.3 Triangles

A polygonis a closed geometric figure with at least three

line segments for its sides. The points at which the sides

intersect are called vertices.A regular polygonhas sides

that are all the same length and angles that are all the

same measure.

The number of vertices of a polygon is equal to the

number of sides it has.

DEFINITIONS AND CONCEPTS EXAMPLES

Quadrilateral

(4 sides)

Hexagon

(6 sides)

Octagon

(8 sides)

side

side

side

side

side

vertex vertex

vertex

vertex

vertex

Polygon Regular polygon

Number Name of Number Name of

of sides polygon of sides polygon

3 triangle 8 octagon

4 quadrilateral 9 nonagon

5 pentagon 10 decagon

6 hexagon 12 dodecagon

Classifying Polygons

A triangleis a polygon with three sides (and three

vertices).

Triangles can be classified according to the lengths of their

sides.

Tick marksindicate sides that are of equal length.

Equilateral triangle

(all sides of

equal length)

Isosceles triangle

(at least two sides of

equal length)

Scalene triangle

(no sides of

equal length)