I like to show my students Perigal’s Puzzle. Basically, it is a proof without words of the Pythagorean Theorem. First, you start with a right triangle.
Then, you have the areas of each side: a^2, b^2, and c^2. To make things easy, I will call them Square A, Square B, and Square C.
Cutting apart Square B, you can fit Squares A and B to be the same as Square C.
BAM! The Pythagorean Theorem works.
Here is a file that you can download for easy cutting :) Also, if cutting paper isn’t your style, there is a YouTube video you can show.