The Pythagorean Theorem I: Two Proofs and a Corollary

From a channel Lumen includes in full: What the Hectogon? is a small maths channel working through geometry, trigonometry and calculus questions with the full reasoning shown, including Summer of Math Exposition entries.

A 17-minute video from What the Hectogon?'s catalogue; the title names its topic.

Video by What the Hectogon?, played through YouTube's embedded player.