For me, the visual proofs of simple sums (like The sum of the first n odd natural numbers is n²) works pretty well for me. For the more geometry-based ones whe

For me, the visual proofs of simple sums (like The sum of the first n odd natural numbers is n²) works pretty well for me. For the more geometry-based ones where you have move triangles around and so, it's often not obvious to me that two angles that look the same really always are the same, and that things that add up to rectangle do so reliably, independently of the actual angles used in the examples. I guess in these cases, a more parameterized, interactive version would work better, where you can use sliders to adjust some of the angles and lengths used. That should make it much more obvious that it's not just an artifact of particular angles used in an example.