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Angles Formed by Parallel Lines Cut by a Transversal

In the applet below, AB || CH (line AB is parallel to line CH). Line DE is a transversal. There are 8 angles formed at the intersections of the lines - do you see them?
  1. Drag point A or B to change the location & direction of both parallel lines.
  2. Drag point D or E to change the location & direction of the transversal.
As you change the lines, pay attention to the measurements of the 8 angles that are marked.
  1. Which angles are always the same size?
  2. Which angles are always supplementary (add up to 180°)?

Parallel Lines cut by a Transversal