The following worksheet should be cut in half (The top two proofs are the same as the bottom two). Great for saving paper! These are two great proofs for introducing the definition of alternate interior angles.
Students must be aware of the reflexive property and vertical angles property and midpoint in order to be successful on these two proofs.
The proof is already somewhat filled out. Blanks are provided to ease students into the new definition. I used the clouds to provide a place to clarify which postulate they were using (SSS, SAS, ASA, or AAS)