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 Nov 13, 2019 Ask Uncle Colin: An Exponential Limit Feb 6, 2019 Ask Uncle Colin: Computing $\sqrt{2}$ Jun 28, 2017 Ask Uncle Colin: Trouble in Sector ABC Jan 30, 2013 Book review: Alex's Adventures In Numberland by Alex Bellos subscribe via RSS