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 Dec 4, 2019 Ask Uncle Colin: A proof Jul 24, 2019 Ask Uncle Colin: A problem of squares and powers Feb 1, 2017 Ask Uncle Colin: A Triangle That's Not As Nice As It Looks Mar 1, 2012 Quotable maths: Erdős subscribe via RSS