Brahmagupta's theorem states that if a
cyclic quadrilateral ABCD has perpendicular diagonals, then the
perpendicular to a side from the point of intersection of the
diagonals always bisects the opposite side. See also:
Corollary.
Brahmagupta (598–668) was an Indian
mathematician and astronomer who discovered a neat formula for
the area of a cyclic quadrilateral.
