When are two isometries the same? | From Euclid to Escher class 1 part 2

Having understood what an isometry is and how mathematicians use them to talk about symmetry, the important question becomes: how can we tell when two isometries are the same. It turns out there is an elegant answer to this question which David discusses and proves.

Music: Variation 1 from the Goldberg Variations by JS Bach, performed by Kimiko Ishizaka (CC0 no copyright).