Classifying Triangles by Side Lengths and Angles

Melissa McGarity

Objectives: Students discover the properties of equilateral, isoceles, scalene, right, acute, and obtuse triangles. Students will use the properties of triangles to classify them.

Materials: GSP files

Student exploration Worksheet for GSP files "Triangle/sides" and "Triangle/angles."

Classifying Triangles by Side Lengths and Angles

Instructions: Open the GSP file "Triangles/sides" to explore questions 1 - 3.

1. Equilateral Triangles

Measure all of the side lengths of all of the triangles listed as Equilateral triangles. What do you notice about the relationships between the sides of each triangle?

Also measure the angles of all the triangles in this section. What do you conclude about the angles of equilateral triangles?

What can you say about the sides of equilateral triangles?

What can you say about the angles of equilateral triangles?

2. isoceles Triangles

Measure all of the side lengths of all of the triangles listed as isoceles triangles. What do you notice about the relationships between the sides of each triangle?

Also measure the angles of all the triangles in this section. What do you notice about the angles of isoceles triangle?

What can you conclude about the sides of isoceles triangles?

What can you conclude about the angles of isoceles triangles?

3. Scalene Triangles

Measure all of the side lengths of the triangles listed as Scalene triangles. What do you notice about the relationship between the sides of each triangle?

What can you conclude about the sides of scalene triangles?

Instructions: Open the GSP file labeled "Triangles/angles" to answer questions 4 - 6.

4.. Right Triangles

Measure all of the angles of the triangles listed in the right triangle section.

What can you conclude about right triangles?

5. Acute Triangles

Measure all of the angles of the triangles listed in the acute triangle section.

What can you conclude about acute triangles?

6. Obtuse Triangles

Measure all of the angles of the triangles listed in the obtuse triangle section.

What can you conclude about obtuse triangles?

7. There are three ways to classify triangles by side length. List the three ways to name triangles according to the lengths of their sides.

8. There are three ways to classify triangles by angle measurements. List the three ways to name triangles according to their angle measurements.