The equation A^T A = I describes a property of orthogonal matrices. Here, A^T represents the transpose of matrix A , and I is the identity matrix. This relationship indicates that the rows (or columns) of A are orthonormal, meaning they are both orthogonal (perpendicular) and normalized (having a length of one). In practical terms, if you multiply an orthogonal matrix by its transpose, the result is the identity matrix. This property is useful in various applications, including computer graphics, signal processing, and solving systems of linear equations, where maintaining the structure of data is essential.