# Quadrilaterals, Theorems and Problems, page 4 of 4

 The Incas used trapezoids for all their windows and doors, which withstand earthquakes well.
 Quadrilaterals: Table of Content (Page 4 of 4) Square Proposed Problem 76: Area of a Circle. Square, Circle, Circular Sector. Proposed Problem 74: Three Intersecting Circles. Cyclic quadrilateral, Angles. Proposed Problem 73: Three Intersecting Circles. Cyclic quadrilateral. Proposed Problem 72: Intersecting Circles. Cyclic quadrilateral, Chords, Parallel. Four Circles Theorem Using TracenPoche Dynamic Software Step-by-Step construction, Manipulation, and animation. Proposed Problem 63: Heptagon Regular, Side and Diagonals. Proposed Problem 62: Square Diagonal, Inscribed Circle. Arbelos, Inscribed Circle and Concyclic Points Cyclic Quadrilateral. Proposed Problem 57: Angle bisector, circles Cyclic Quadrilateral. Proposed Problem 55: Angle bisector, circles Cyclic Quadrilateral. Eyeball Theorem: Animated Angle to Geometry Study. Eyeball to Eyeball Theorem Presentation: "Animated Angle to Geometry Study I & II." 46th Annual Georgia Mathematics Conference, Extreme Makeover: Mathematics Edition!, Rock Eagle, October 20-22, 2005, Varignon and Wittenbauer parallelograms. Quadrilateral: midpoints and trisection points of the edges. Van Aubel's Theorem. Quadrilateral with Squares. Proof with animation. Brahmagupta's Theorem Cyclic quadrilateral. Brahmagupta's Corollary Cyclic quadrilateral. Brahmagupta's Formula  Area of a cyclic quadrilateral. Brahmagupta Formula Extension Area of any quadrilateral. Newton's Theorem: Newton's Line. Circumscribed quadrilateral, midpoints of diagonals, center of the circle inscribed. Puzzle of the Newton's Theorem: 50 pieces of circles. Sangaku Problem. The incenters of four triangles in a cyclic quadrilateral form a rectangle. Complete Quadrilateral Theorems Presentation: "Animated Angle to Geometry Study I & II." 46th Annual Georgia Mathematics Conference, Extreme Makeover: Mathematics Edition!, Rock Eagle, October 20-22, 2005, Kurschak's Tile and Theorem. Jozsef Kurschak (Hungary, 1864-1933) An elegant and a purely geometric way of finding the area of a regular dodecagon. Proposed Problem 33. Triangle and quadrilateral. Proposed Problem 35. Incenters and Inradii in Cyclic Quadrilateral. Proposed Problem 42. Angles and triangles. Go to Page: Previous | 1 | 2 | 3 | 4 | Next
 Home | Geometry | Polygon | Trapezoid |Triangle and Squares | Email | By Antonio Gutierrez Last updated: May 7, 2009