Chris Luke, AC for Derby, Northamptonshire and Rutland
![](https://amsp.org.uk/app/uploads/2022/08/march-2019.png)
The diagram shows a right-angled triangle and its incircle. The lengths of the sides of the triangle are a,b,c where c is the length of the hypotenuse. The diameter of the incircle is d. Show that a + b = c + d.
Does this diagram help?
![](https://amsp.org.uk/app/uploads/2022/08/november-puzzle-1.png)