# Activities

• • • ##### Subject Area

• Math: Geometry: Triangles

• ##### Author 9-12

15 Minutes

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

TI-SmartView™

## Got the sum of remote interior angles equal to the measure of the exterior angle? with Cabri Jr.

#### Activity Overview

Draw a triangle with exterior angle. Measure the exterior angle and each remote interior angle. Use the Alpha hand to check that the sum of the remote interior angles is always equal to the exterior angle.

#### Before the Activity

Students need basic knowledge of selecting Cabri Jr. tools, Clear key, Alpha key to drag, etc.

#### During the Activity

F2 select Triangle. To draw a Triangle?Press Enter to anchor first vertices. Move curser, and press Enter to anchor second vertices. Move curser, and press Enter to anchor third vertices. Clear to exit Triangle tool. F2 use the Line tool to make one of the sides of the triangle extend in both directions. Be sure the vertices of the triangle are ?shimmering? or selected when creating the triangle side that extends. F5 select Measure> Angle to display the measurements of each remote interior angle and the exterior angle. Students must select the vertex as the second point to measure each angle correctly. As the measurements in degrees are displayed drag each measurement next to its angle. F5 select Calculate choose the displayed measurement of one of the remote interior angles Plus the other remote interior angle. When the sum is displayed, drag it between the two remote interior angles. Select a side or vertices and use the Alpha hand to drag. The sum of the remote interior angles stays equal to the measure of the exterior angle.

#### After the Activity

For added accuracy?select the measurement of the exterior angle (a line under the numbers ?shimmers? when selected) hit the Plus key twice. Select the sum of the remote interior angles, hit the Plus key twice. Now select a side of the triangle or one of its vertices, and Alpha hand drag. They are equal to the hundredths place. Note?to remove the decimals select a displayed value and hit the Minus key. Take a 1to10. A 1to10 is a way to monitor the understanding of a class. Ask the students to 2nd quit Cabri Jr (or any APP), and have only a black curser on the calculator. Ask a question about their understanding of remote interior and exterior angles. Students place a 1 to 10 on their screen. 1 equals the need for further explanation, and 10 equals total understanding of the concept. Screen Capture in TI-Navigator. (Quick Poll can also be used for 1to10)