1. 9.1
Lines and Angles

2. Chapter 1 / Whole Numbers and Introduction to Algebra
Planes
A plane is a flat surface that extends indefinitely.
Plane
Space extends in all directions indefinitely.

3. Chapter 1 / Whole Numbers and Introduction to Algebra
Points
The most basic concept of geometry is the idea of a point in space. A point has no length, no width, and no height, but it does have location. We will represent a point by a dot, and we will label points with letters. A
Point A

4. Lines, Segments, and Rays
Line AB or AB A B
Line Segment AB or AB A B
Ray AB or AB A B

5. Angles
An angle is made up of two rays that share the same endpoint called the vertex. A B C x
Vertex
The angle can be named ABC, CBA, B, or x.
The vertex is the
middle point.

6. Chapter 1 / Whole Numbers and Introduction to Algebra
Angles
An angle can be measured in degrees. There are 360º (degrees) in a full revolution or full circle.
360º

7. Chapter 1 / Whole Numbers and Introduction to Algebra
Classifying Angles
Name
Angle Measure
Examples
Acute Angle
Between 0° and 90°
Right Angle
Exactly 90°
Obtuse
Angle
Between 90° and 180°
Straight Angle
Exactly 180º

8. Examples
For the figure shown, use symbols to name a line, two rays, and a segment.
In this figure, XY is 12.3 inches and XZ is 20.1 inches. Find YZ.

9. Chapter 1 / Whole Numbers and Introduction to Algebra
Polygons
A polygon is a flat figure formed by line segments connected at their ends.
Geometric figures such as triangles, squares, and rectangles are called polygons.
triangle
square
rectangle

10. Perimeter
The perimeter of a polygon is the distance around the polygon.

11. Example
Find the perimeter of this figure. All angles are right angles. Dimensions are in centimeters (cm).