Erdmann's theorem

Erdmann's theorem states that when a quadrilateral (a four-sided shape) is inscribed in a circle, the diagonals (lines connecting opposite corners) intersect at a point where the pairs of angles formed are equal. In other words, the angles created where the diagonals cross are the same as the angles at the corners of the quadrilateral that are directly connected by the diagonals. This property helps in understanding the relationships between the angles within cyclic quadrilaterals and is useful in solving geometric problems involving circles and polygons.