Education Technology

Activities

• Subject Area

• Math: Geometry: Triangles

9-12

60 Minutes

• Device
• TI-83 Plus Family
• TI-84 Plus
• TI-84 Plus Silver Edition
• Software

Cabri Geometry™
TI Connect™

• Accessories

TI Connectivity Cable
Unit-to-Unit link cables

• Other Materials
This is Activity 8 from the EXPLORATIONS Book:
Exploring The Basics Of Geometry With Cabri

Midsegment of a Triangle

Activity Overview

Students explore the properties of triangles formed by connecting the midpoints of two sides of a triangle, and examine the relationship between the two triangles. They study the Triangle Midsegment theorem.

Before the Activity

Install the Cabri™: Jr. App on the students' graphing calculators using one of these two methods:

• TI-Connect™,  a TI Connectivity Cable, and the Unit-to-Unit Link Cable
• TI-Navigator™  "send to class" feature
• See the attached PDF file for detailed instructions for this activity
• Print pages 31 - 35 from the attached PDF file for your class
• During the Activity

Distribute the pages to the class.

Follow the Activity procedures:

• Draw a triangle and label its vertices
• Construct a midsegment by joining the midpoints of two sides of the triangle
• Check whether the midsegments are parallel to their opposite sides
• Measure the length of the midsegment and the length of the opposite side of the original triangle
• Observe that the midsegment is half the length of the opposite side
• Drag one of the vertices to alter the triangle
• Verify that for all triangles, a midsegment is parallel to the opposite side and length of the midsegment is half that of the opposite side
• Find the perimeter and area of the original triangle and the midsegment triangle
• Alter the triangle and tabulate the perimeter and area of the original triangle and the midsegment triangle
• Observe that the perimeter of the midsegment triangle is half the original triangle
• Note that the area of the midsegment triangle is one fourth that of the original triangle
• Measure the angles of the midsegment triangle and the original triangle
• Alter the triangle to create an acute triangle, an obtuse triangle, and then a right triangle
• Notice that the type of triangle formed by the midsegments is the same type of triangle as the original triangle
• After the Activity

Review student results:

• As a class, discuss questions that appeared to be more challenging
• Re-teach concepts as necessary