Geometry Tutor: Classifying and Defining Triangles and Their Parts

Here are some ideas of how to introduce the triangles unit from Geometry to 9th graders.
Here are some lesson ideas dealing with classifying triangles and their parts.

Geometry Triangles 55 minutes

Congruent Triangles Lesson #1: Classifying and Defining Triangles and their parts

Context

This is the first lesson of the unit. A lot of information in this first section is strictly definitions, so most students will be fairly unfamiliar with some of the terms discussed in this lesson. However, students will have to set up some pretty simple algebraic equations to find the measures of missing angles in triangles. Students used this algebra in Algebra I and in the first three chapters of Geometry.

Objectives

Students should be able to classify triangles by sides and angles.

Students should understand the parts of triangle that make up its sides and angles.Resources, Media and Technology

- Class set of rulers and protractors

Procedures

Day 1

1. Class will begin with an explanation of the pretest. Then I will give out the pretest.

2. After all tests have been handed in, I will start the unit by drawing types of triangles on the board and I will ask the students to see if they can come up with any of the names off the top of their head.

3. For the ones they don't know, I will them and write all the types of the triangles on the board. I will tell them this is one way to classify triangles and that is by sides.

4. Next, I will do the same thing for classifying triangles by angles. I will emphasize there are TWO ways to classify triangles: by sides and angles.

5. Next, I will draw an isosceles and right triangle on the board. I will use these diagrams to define the legs, hypotenuse and bases of triangles.

6. After defining these, I will draw some triangles on the board and I will give the students a moment to think of what type of triangles they are. Then, I will call on students to give me the names of the triangles.