I was at a table full of kindergartners playing with triangles, trapezoids, and concave hexagons. We were building and chatting. They wanted to know if I wanted to hear them sing in French. I said yes. The sweetest two minutes ensued as this table’s Frere Jacques spread to the next and then the next, and soon the whole classroom was singing and doing math.
A few minutes later I made this.
And then I went scrambling for my notebook.
Yup. Sure enough. 
Overthinking my teaching 
Love this! My advanced fifth graders have recently learned the Pythagorean theorem – this will challenge them to see how you came up with your equation. Thank you!
Imagine the children have a large sheet of red paper and they have paper triangles they can move around atop the sheet of red paper.
Then the Pythagorean theorem ‘pops out’ even more clearly.
I reveal how at http://www.jonathancrabtree.com/mathematics/a-proof-of-pythagoras-via-the-chinese-chou-pei-suan-ching/