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 26, 2020 Ask Uncle Colin: A Trigonometric Identity Jul 29, 2019 Futility Closet, Fibonacci and Quadratic Residues Jul 4, 2013 Wrong, but Useful: Episode 4 Aug 29, 2012 Five ways that maths is stoopid subscribe via RSS