This lecture covers geometric transformations in R2 and R3, focusing on functions mapping vectors to their transformations, including reflections and rotations. The instructor demonstrates how to determine the expression of a transformation function and the inclination of axes. The lecture also explores the concept of symmetry and orthogonal reflections, providing step-by-step examples of applying transformations in practical scenarios, such as billiards. Through detailed explanations and mathematical derivations, students will gain a solid understanding of how geometric transformations operate in different dimensions.