U1L12 Defining Translations

This lesson continues the theme of revisiting rigid transformations students explored on coordinate grids in previous grades and refining their understanding to define those transformations more generally without coordinate grids. The concept of a directed line segment is introduced to give students language for efficiently describing the direction and length of a translation. Students know the term line segment, and so the phrase directed line segment builds on a concept they already know and connects it to the concept of translations. The word vector is purposely avoided because the geometric interpretation of a vector should arise as a consequence of future work with vectors, not as a definition. Students make arguments and critique the reasoning of others when they explain why translating a line segment results in a parallelogram (MP3). This argument leads to the Parallel Postulate. This activity includes lesson summary videos and practice problems.

By JOEL NELSON