# Intro: GeoGebra skills, terms, vocabulary & postulates

Author:
Zawierucha

The objectives of this activity: With the GeoGebra app: 1. you will become familiar with some of the tools used in GeoGebra. 2. you will explore what you can and can't change once you have constructed a figure. 3. You will work with 2 of the three undefined terms, point & line, in order to illustrate some postulates. With the follow-up questions: 1. You will review and extend your understanding of the postulates and definitions you encountered 2. You will review the vocabulary used in this activity. 3. You will use the Applet to make some observations and write some conclusions. What you should you do in your notebook: 1. Add any new vocabulary to your vocabulary section. 2. Write down questions and correct answers for any questions that you weren't sure about and/or got incorrect. 3. Keep track of new observations and facts that helps you extend your understanding of the material covered.

## Getting comfortable with some GeoGebra tools, review some postulates and new vocabulary.

Part 1 - what you will do on the applet below ***FYI: once you have drawn something always go back to the move tool (or hit esc on keyboard) in order interact with what you have on the screen. Move the figures around. Notice what you can and can't change*** Directions: A. Two undefined terms: a point and a line 1. Use the point tool and plot two points, then use the line tool to construct a line. What you have just done is illustrated the following postulate: "Through 2 points there is exactly one line" Definition, postulate -A geometric statement whose truth is assumed without a proof. Clear your screen B. Subsets of a line: the ray and a segment. ﻿vocabulary: ray, segment, midpt. (of a segment) 1. Use the ray tool to draw a ray, the first point that is illustrated is its endpoint. 2. Use the segment tool to draw a segment. 3. Use Segment with Given length tool to draw another segment. 4. Use the midpoint tool to locate the midpoint on each of your segments. ﻿ a. For each of the segments constructed in step 1 & 2: use the distance/length tool to measure the length of the two segments formed by the midpoint. b. Construct a line. Can you get a midpoint for your line? Clear your screen C. Circles constructed two ways. Vocabulary: circle, center, point on a circle, radius. 1. Construct your first circle using the Circle with Center through point* tool - *that point is on the circle. 2. Construct your 2nd circle using the Circle: Center & radius tool Use the move tool to explore what you can and can't change about the 2 circles. 3. First, delete your 2nd circle. Construct a radius for your 1st circle using the segment tool. 4. Construct a 2nd radius for that circle but this time use Segment with Given length tool And instead of writing in a specific value enter the name of endpoints of the first radius for example AB - the capital letters side by side is the symbol that stands for: "the length of segment AB". Do this once more. You will now have 3 radii (plural for radius) for your circle. 5. Use the distance or length tool to get the length of all three radii. Clear your screen D. Another postulate. 1. use the line tool to construct 2 lines that intersect. 2. Use the intersect tool to get their point of intersection. You have illustrated the postulate: "if two lines intersect, then they intersect in exactly one point."

## Some of the questions will talk about congruence. Watch this short video before you answer the questions.

We encountered 2 postulates in this activity: 1. Through 2 points there is exactly one line 2. if two lines intersect, then they intersect in exactly one point. In your own words describe what each postulate is saying.

## 2. Definition

circle is all points in the same plane that lie at an equal distance from a center point. A radius of a circle is a segment whose endpts. are the center of the circle and a point on the circle. A diameter is a chord that contains the center of the circle. Define, chord (of a circle)

## 3. Definition

Define, ray.

In plane geometry we have three undefined terms one is "plane" ( a 2-dimensional surface that extends out indefinitely into space), what are the other two undefined terms mentioned in this activity.

## 5. Definition

Define, postulate.

Define, segment.

## 7. Explain

Explain why the following statement must be true: in a circle or in congruent circles, radii or diameters are congruent. (make sure to watch the video that explains congruent figures)

## 8. Fill-in

a. A circle has ________ radii and diameters. b. A segment has ________ midpoint(s). c. A line has ______ midpoint(s). possible answer choices: zero, one, two, three, infinite (unlimited)

Define, midpoint

## 10. Definition

Define, congruent (figures)

## 11. Vocabulary

﻿List all the vocabulary used in this activity.