# Notation & Symbols in Plane Geometry

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• 0:04 Geometric Notation
• 0:52 Linear Relationships
• 1:12 Parts of a Line
• 1:40 Geometric Figures
• 2:39 Units of Measure
• 3:21 Lesson Summary
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Lesson Transcript
Instructor: Melanie Olczak

Melanie has taught high school Mathematics courses for the past ten years and has a master's degree in Mathematics Education.

In this lesson, we'll discuss how to identify and draw the standard notation for points, lines, and angles, as well as symbols for geometric concepts such as length, measure, parallel, perpendicular, and congruent.

## Geometric Notation

Have you ever wondered how to represent an angle in mathematics? Is there a difference between congruent and equal? What do all those symbols in geometry even mean?

The purpose of geometric notation is to identify geometric figures or shapes and the measures of those figures, such as their lengths or sizes. Let's start with some basic geometric figures.

A point is a location. It can be placed in the coordinate plane with coordinates (x, y) to signify the location, or it can be placed in space with just a point or a capital letter.

A line is a straight series of connected points. Lines do not have an end, as they continue in both directions. We show that they do not end by placing arrows at each end. To identify and label a line, choose any two points on the line and place the line symbol above them.

## Linear Relationships

Parallel lines are those lines that never cross or intersect. Perpendicular lines intersect at a right angle. Rather than writing out the words 'parallel' and 'perpendicular,' we use geometric notation.

The symbol for two parallel lines is two vertical lines.

The symbol for two perpendicular lines is an upside-down T.

## Parts of a Line

A line segment is a section of a line between two endpoints. To label a line segment, identify the two endpoints and place the segment symbol above them.

Another part of a line is called a ray. A ray has one endpoint and continues in one direction forever. To express it, use the first letter as the endpoint and the second letter as any point further along the ray.

In this image, ray AB is not the same as ray BA because they have two different end points.

## Geometric Figures

A plane is a flat surface that exists in space. Think of a plane as the ceiling, floor, or wall of a room. Planes can intersect with each other, or they may never touch. A plane is named using three non-collinear points, which means that it's not possible to draw a line through the points.

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