The quadrilateral ABCD is inscribed in the circle and the lengths of the sides BC and DC are equal, and the length of the side AB is equal to the length of the diagonal AC. Let the point P be the midpoint of the arc CD, which does not contain point A, and Q is the point of intersection of diagonals AC and BD. Prove that the lines PQ and AB are perpendicular. geometryperpendicularequal segmentscyclic quadrilateralarc midpointChampions Tournament