Pythagoras, Pythagorean, Euclidean, Gravitational Lensing, Symmetry.
start a new class, being physics or math, I dedicate several minutes to this subject. According to some articles, there are circa 350 proofs of the Pythagorean Theorem, some of them you can find here. I will present my favorite, which is a combination of simple geometry and algebra. Figure 1: Four