Theorem. If a, b, c, d denote the lengths of the sides; p, q the lengths of the diagonals, R the circumradius, and Q the area of a cyclic quadrilateral, the
Theorem. If a, b, c, d denote the lengths of the sides; p, q the lengths of the diagonals, R the circumradius, and Q the area of a cyclic quadrilateral, the