Make a centre crease down the length of the paper then open it up.
Next fold one corner over and onto the centre crease so that the fold line passes through the corner next to it (on the short side of the paper).
The diagram shows three angles a, b and c.
How many ways can you prove that a + b = c?
What other interesting properties can you find?
When this activity was originally published on NRICH, two boys from Madras School in St Andrew’s, Scotland sent […]