Name:___________________________________
Parallel Lines
Date:_______ Period:_____
Ms. Anderle
Parallel Lines
Recall: Parallel lines are two lines that never intersect.
*There are special relationships that form when a parallel line is cut by a transversal.*


Alternate Interior Angles: If two parallel lines are cut by a transversal, then each
pair of alternate interior angles is congruent.
Alternate Exterior Angles: If two parallel lines are cut by a transversal, then each
pair of alternate exterior angles is congruent.
Parallel Lines in Proofs:
Examples:
1.
Given: AB || CD
AB  CD
Prove: ABD  CDB
2.
Given: WX || TV
Y is the midpoint of XT
Prove: WX  TV
3.
Given: AD || BC
AD  BC
Prove: AB  DC
Proving Segments Parallel:
If you are asked to prove segments parallel you must first find a pair of alternate
interior angles – then you can say that the segments are parallel. You might have to use
CPCTC to prove the angles congruent.
1.
Given: ΔABC and ΔEDC,
C is midpoint of BD and AE
Prove: AB || DE
2.
Given: AB  DC
AD  BC
Prove: AD || BC