A proof without words Nov 23, 2020 Via nRICH: A circle touches the lines OA extended, OB extended and AB where OA and OB are perpendicular. Show that the diameter of the circle is equal to the perimeter of the triangle. $\blacksquare$ A selection of other posts Feb 10, 2020 Proofs Aug 22, 2018 Ask Uncle Colin: Two triangles Jul 12, 2017 Ask Uncle Colin: A Polar Expression Sep 6, 2012 Quotable maths: Roberts subscribe via RSS