Given: ABCD is a parallelogram.


Prove: ∠A ≅ ∠C and ∠B ≅ ∠D


Parallelogram A B C D is shown.


By the definition of a ▱, AD∥BC and AB∥DC.


Using, AD as a transversal, ∠A and ∠

are same-side interior angles, so they are

. Using side

as a transversal, ∠B and ∠C are same-side interior angles, so they are supplementary. Using AB as a transversal, ∠A and ∠B are same-side interior angles, so they are supplementary.


Therefore, ∠A is congruent to ∠C because they are supplements of the same angle. Similarly, ∠B is congruent to ∠

answers: d, supplementary, bc, d

Given ABCD is a parallelogramProve A C and B DParallelogram A B C D is shownBy the definition of a ADBC and ABDCUsing AD as a transversal A and are sameside int class=