This lecture covers the concept of matrix inversion, defining a matrix A as invertible if there exists a matrix B such that AB = BA = I. The uniqueness of the inverse of A is also discussed, along with the properties of determinants for matrices A and B. The lecture presents the proof of the existence of the determinant and explores the function det(AB). Various propositions are introduced, demonstrating the relationship between the determinants of A, B, and AB. The lecture concludes with practical examples and remarks on efficient methods for calculating inverses.