The goal of this activity is to have students prove that when given parallel lines alternate interior angles are congruent, alternate exterior angles are congruent, and consecutive interior angles are supplementary. This activity provides scaffolding to allow students to generate the proofs of these theorems. The theorems should then be formally stated and recorded for future use.
This activity includes a formal two-column proof outline for each of the 3 theorems indicated above. The statements are completed and students are given reason banks from which to select the appropriate reasons needed to complete the proofs. More reasons are provided for each proof than are necessary. This requires students to analyze the statements and select the correct reason rather than simply using process of elimination. This activity can easily be differentiated by removing some of the reason bank possibilities or removing some of the completed statements and requiring students to fill them in.
Suggestion for Use: Copy a class set of the three proof outlines and the reason banks. Cut apart the reason banks for each proof and paper-clip them together. Give pairs of students one copy of the proofs and a copy of each reason bank. Students can move the reasons around and place them in the correct location to complete the proofs. This allows for easy correction of mistakes and repeated use of the activity.