Question

prove that a cyclic Parallelogram is a rectangle

Answer 1

✋✋✋✋✋✋☺☺☺
Opposite angles in a parallelogram are congruent, while opposite angles in a cyclic quadrilateral are supplementary. Congruent supplementary angles are right angles, so opposite angles in a cyclic parallelogram are right angles. Thus all four angles are right angles, and it's a rectangle.

Answer 2

Opposite angles in a parallelogram are congruent, while opposite angles in acyclic quadrilateral are supplementary. Congruent supplementary angles are right angles, so opposite angles in acyclic parallelogram are right angles. Thus all four angles are right angles, and it's a rectangle.