Alternate Interior and Vertical Angles

Lines a and b are parallel lines. Lines c and d are transversal (cut across two or more parallel lines).

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Alternate Interior Angles
1. Locate the alternate interior angles in the illustration. How many pairs of alternate interior angles is there?
2. Move point E around; what do you notice about the alternate interior angles?
3. Move points D, F, and G around; what do you notice about the alternate interior angles?
4. Move line a around; what do you notice about the alternate interior angles?
5. What conclusion can you draw about alternate interior angles of parallel lines?

Vertical Angles
1. Locate the vertical angles in the illustration.
2. Move points D, E, F, and G around; what do you notice about the vertical angles?
3. Move line a around; what do you notice about the vertical angles?
4. What conclusion can you draw about vertical angles?
5. Can you locate another pair of vertical angles?
6. Do the lines creating vertical angles have to be transversals for the vertical angles to be equal?

Tammy Short, October 18, 2010, Created with GeoGebra