We start with three triangles the same size and shape. I've coloured them differently but that's not important. I've labelled each corner for you.
Using three pieces of thick paper or card on top of each other you can carefully cut out a triangle shape so that you'll have three identical triangles.
Look how I've started to put the different corners together;
Put your corners together completely so that they close up and have no gaps or overlapping.
Try it again with a new set of three triangles.
You could try it many times with very different triangles.
What can you say about it?
What if you use two sets of three triangles together?