Advanced vertically opposite angles

Craig Barton

Author: Ben Gordon

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 so that the two diagrams look the same
  • I ask students to pause and reflect on what the page shows
  • I then reveal line segment EF, hide angle CEB,show angle FEB
  • I ask students to reflect on what has changed and predict what will happen when I reveal the size of angle CEF
  • 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 angles that are revealed
  • Vary the angles that are hidden
  • Vary the angle of the line segments
  • Vary the length of the line segments
  • Vary by hiding/revealing lines EF and EL
  • Vary by hiding all angles and including variables instead

Click here to open sheet full screen in Geogebra