Triangle

Content Objective:

Students will rediscover the method of finding the perimeter and area of regular triangles.

Materials:

Rulers for pairs, triangle perimeter worksheet, triangle area worksheet

Procedure:

Perimeter

1. Collectively recall the definition of perimeter given on review day. Have students get into pairs and distribute perimeter worksheet. Once worksheet is complete and students have compared their answers, ask the class as a whole the following questions:

What do you notice about the side lengths of our triangles?

What happens to the perimeter when the side lengths are changed?

Is there a way to find the perimeter of a regular triangle without measuring all three sides?

2. Demonstrate using Geometer's Sketchpad the properties of the side lengths of regular triangles. Click here to use the GSP file and animate the triangle.

Area

1. Collectively recall the definition of area given on review day. Now, have students get back into pairs and distribute area worksheet. Once worksheet is complete and students have compared their answers, ask the class as a whole the following questions:

What do you notice about the base of our triangles? Is there only one side of our triangles that can be considered a base?

What happens to the area when the base lengths are changed? What happens to the area when the altitude length is changed?

How is length of the altitude related to the length of the base?

Is there a way to find the area of a regular triangle with one side length and the altitude length?

2. Demonstrate using Geometer's Sketchpad the properties of the base and altitude of regular triangles. Click here to use the GSP file and animate the triangle.