U
Proving the Parallelogram Side Theorem
Given: ABCD is a parallelogram.
Prove: AB CD and BC DA
Angles Segments Triangles Statements
Reasons
given
def of parallelogram
unique line postulate
def. of alt interior angles
Statements
Reasons
Demo
Intro

1. 2. ∠b and ∠y are right angles. 3.? 4.? which two statements are missing in steps 3 and 4? ∠x ≅ ∠c △abc ~ △zyx by the sas similarity theorem. ∠b ≅ ∠y △abc ~ △zyx by the sas similarity theorem. = 2 △abc ~ △zyx by the sss similarity theorem. = 2 △abc ~ △zyx by the sss similarity theorem.