Explore congruency of vertical angles

Group students in pairs, give them the calculators.

1. Direct students to draw a line using Cabri. 2. Draw a second line that starts from point 1 of the first line. 3. Use the measurement tool to measure the 4 angles that are formed by the 2 intersecting lines. 4. What do you notice about the angle measurements? 5. Grab the second point that you used to draw one of the lines. Rotate the line about the point of intersection. 6. What do you notice about the measurements of the angles? 7. The angles that have the same measurements are called vertical angles. 8. Why is the name vertical angles an appropriate name for these pairs? 9. Play with rotating the second line about the point of intersection. 10. WHen are all 4 anlge measurements the same? 11. Find measurement such that: a. 1 angle = 8 times the other angle b. 1 angle = 5 x the other angle c 1 angles = 2 x the other angle.

I ask the students to discuss the name, vertical angle, and to write the relationship of vertical angles in their notes. THey convert the visual angle 1 = 3 x angle 2 into algebraic format.