The diagonal point triangle revisited - Martin Josefsson We derive a formula for the area of the diagonal point triangle belonging to a...
Properties of equidiagonal quadrilaterals - Martin Josefsson We prove eight necessary and sufficient conditions for a convex quadrilateral to...
Angle and circle characterizations of tangential quadrilaterals - Martin Josefsson We prove five necessary and sufficient conditions for a convex...
Characterizations of trapezoids - Martin Josefsson We review eight and prove an additional 13 necessary and sufficient conditions for a convex...
Five proofs of an area characterization of rectangles - Martin Josefsson There are a handful of well known characterizations of rectangles, most...
Maximal area of a bicentric quadrilateral - Martin Josefsson We prove an inequality for the area of a bicentric quadrilateral in terms of the...
A new proof of Yun's inequality or bicentric quadrilaterals - Martin Josefsson We give a new proof of a recent inequality for bicentric...
Similar metric characterizations of tangential and extangential quadrilaterals - Martin Josefsson We prove five necessary and sufficient...
Characterizations of orthodiagonal quadrilaterals - Martin Josefsson We prove ten necessary and sufficient conditions for a convex quadrilateral...
The area of the diagonal point triangle - Martin Josefsson In this note we derive a formula for the area of the diagonal point triangle belonging...
When is a tangential quadrilateral a kite? - Martin Josefsson We prove 13 necessary and sufficient conditions for a tangential quadrilateral to...
The area of a bicentric quadrilateral - Martin Josefsson We review and prove a total of nine different formulas for the area of a bicentric...
More characterizations of tangential quadrilaterals - Martin Josefsson In this paper we will prove several not so well known conditions for a...
Characterizations of bicentric quadrilaterals - Martin Josefsson We will prove two conditions for a tangential quadrilateral to be cyclic....
Calculations concerning the tangent lengths and tangency chords of a tangential quadrilateral - Martin Josefsson We derive formulas for the...
On the inradius of a tangential quadrilateral - Martin Josefsson We give a survey of known formulas for the inradius r of a tangential...
