This type of activity is known as Demonstration. Please read the guidance notes here, where you will find useful information for running these types of activities with your students.

1. Demonstration

• I display the Geogebra page in silence with all information revealed
• I ask students to pause and reflect on what the page shows
• I then hide the angle labels on the second triangle by clicking the check-boxes
• I move one of the vertices of the second triangle to a new position
• I ask students to reflect on what has changed and predict what will happen when I reveal the size of a given angle – will it be bigger than in the first diagram or smaller? Could they guess the size of it?
• I repeat for a second angle
• I then pause and ask students if they can predict exactly what the third angle will be
• I continue the process, always changing one thing from the original diagram, and always giving students an opportunity to pause, reflect and predict
• At the end I ask students to discuss the rule with their partners, and then we have a class discussion

2. Possible variations

• Vary the position of each point
• Vary the orientation of the shapes
• Create isosceles triangles
• Create scalene triangles

Click here to open sheet full screen in Geogebra