Angles formed when a transversal intersects parallel lines

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Estimated Time

90 minutes

Prerequisites/Instructions, prior preparations, if any

  1. The students should have prior knowledge of parallel lines , transversal, angles and types of angles formed when a pair of parallel lines are intersected by a transversal.
  2. They should know what the terms interior, exterior, adjacent, alternate, consecutive, congruent, linear and corresponding mean.
  3. Students should know the definition of complementary angles, supplementary angles, and congruent angles.
  • Multimedia resources :


  • Website interactives/ links/ / Geogebra Applets :


Materials/ Resources needed

Laptop, geogebra file, projector and pointer.

Process (How to do the activity)

  1. Reiterate that when a transversal intersects parallel lines, several pairs of congruent and supplementary angles are formed.
  2. Have students draw two parallel lines and a third line(transversal) intersecting those two lines on their own paper. Direct them to think about any angle relationships they see. Have them discuss their conjectures with a partner.
  3. The teacher can next project the GeoGebra worksheet and discuss about types of angles and their relationships with the class .
  4. Finally the teacher and students can summarize together the angle relationships.

Linear pair of angles - adjacent and supplementary

Vertical angles - congruent

Corresponding angles -congruent

Alternate interior angles - congruent

Same side interior angles - supplementary

Alternate exterior angles - congruent

Same side exterior angles - supplementary

Developmental Questions (What discussion questions) :

  1. How many pairs of corresponding angles are there ?
  2. What is true about corresponding angles formed when parallel lines are cut by a transversal?
  3. Compare different pairs of alternate interior angles. What do you notice?
  4. <EGD and <AHF are alternate exterior angles. What is another pair of alternate exterior angles?
  5. Compare different pairs of same-side interior angles. What do you notice?
  6. Compare different pairs of same-side exterior angles. What do you notice?

Evaluation at the end of the activity

  1. What are the characteristics of linear angles (adjacent and supplementary) ?
  2. What do you observe about the angle measures of the linear angles?
  • Question Corner :
  1. What do adjacent , alternate, linear , corresponding and consecutive mean individually
  2. What are complementary angles?
  3. What are supplementary angles ?
  4. What does it mean if two angles are congruent?
  5. What is the complement of 65 degrees
  6. What is the supplement of 70 degrees?
  7. Compare angle relationships formed by parallel lines vs. angle relationships formed by non-parallel lines.