Nice origami proof!

I was going to post my simple proof here, but I didn't see how to insert an image. So I posted the proof on my own Medium account. Here is the link:

I don't know if this is a truly original proof, (in the sense of priority) but it is original for me.

Enjoy!

Something to ponder:

The length of any side of any triangle divided by the sine of the opposite angle can be thought of as a constant for that triangle. What geometrical property is shared by all triangles that have the same sine law constant? This question has a beautiful, intriguing result. Searching for the solution leads to other insights.

I will leave you with that for now. Get back to me if you have beaten your head against the wall beyond toleration, but don't short circuit the exploration process.