Geometric Terms

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SWBAT identify and label objects according to geometric conventions

Big Idea

In this lesson, students will formalize definitions of geometric terms and learn how to label geometric parts correctly in order to communicate their geometric knowledge and ideas.

Do Now

5 minutes

For the Do Now, I have students "turn and talk". Since it is early in the year, it is helpful to explain the procedure for a turn and talk. They discuss the answer to the question, "Why is it necessary to use precise language when describing geometric objects?" The main response is, “So we can understand what someone is talking about without being confused.”  After about 3 minutes, we discuss the answer as a whole group. 


18 minutes

In the Mini-Lesson, students complete a chart with definitions and labeling conventions for line segments, rays, parallel and perpendicular lines, angles and circles (G.CO.1). Students are able to refer back to this chart throughout the course.


At the top of the chart, there are two diagrams. Students can use the number line to understand the concept of “distance along a line” as the “length of a line segment.” I ask, “What is distance from point A to point C?” and “What is the distance from point C to point A?” This diagram helps to illustrate that length is the distance between two points on a line and that it can only be positive.


The second diagram showing circle O, can be used to describe the “distance around a circular arc” as a “part of the circumference of a circle.” Students can label the different parts of the circle, and draw a chord to connect points A and B. Using this chord, identify an “inscribed angle.”  The radii and diameter were added to help students identify the semicircles, major arcs, and minor arcs. It is important for students to understand that the distance around a circle is not the same thing as the degree measure of a circle. When students bring up “360 degrees,” I quickly address it and then move on to length.


After examining the diagrams at the top of the page, we write formal definitions of the terms in the chart. In the notation column, students show the symbols that are used to represent the terms. They draw a picture of the term in the example column.  I always make sure to discuss the difference between the notation for line segments, rays and lines. See the "Geometric Terms Mini-Lesson Answer Key" for the definitions I use. 


It is useful to project the chart on a document camera and have a student fill in the chart for the class.



17 minutes

In the first part of the activity, students practice identifying and labeling geometric parts such as angles, rays, lines, etc. I give the students markers or colored pencils to identify the part. When they refer back to this worksheet in later lessons, the colored parts help them make the connection between the name of the part and the part the name describes.


The second part of the activity consists of identifying parts of a circle. Students use the diagram to name a specific part. There are multiple answers for each question.


After about 12 minutes, I go over the sheet and make sure students are able to correctly identify and label the parts. Students use the document camera to show their results. For the second part, I call on several students for each question in order to get a variety of responses.



5 minutes

Exit Ticket:  Students will identify three line segments, two angles, and one pair of parallel lines from the diagram in the Smartboard presentation.

*It is important to mention that the figure is a square. This helps students to identify a pair of parallel lines. 

After about 4 minutes, we go over some answers. I ask students to come to the Smartboard and identify and label one of the parts they chose.