Given: ABCD is a parallelogram. Prove: ZA = 2C and ZB = ZD
D
С
By the definition of a -,AD // BC and AB / DC.
Using, AD as a transversal, ZA and 2 vare same-
side interior angles, so they are
Using side as a transversal, ZB and ZC are
same-side interior angles, so they are supplementary.
Using AB as a transversal, ZA and B are same-side
interior angles, so they are supplementary
Therefore, ZA is congruent to 2C because they are
supplements of the same angle. Similarly, ZB is
congruent to v
А
B.