Six Diagonals Trick for 3x3 Determinants

From a channel Lumen includes in full: MathDoctorBob, a maths professor, has a large archive of complete course lectures in algebra, calculus, linear algebra and abstract algebra, plus research talks.

A 5-minute video from MathDoctorBob's catalogue; the title names its topic.

Video by MathDoctorBob, played through YouTube's embedded player.