Linear Algebra, Linear Transformation.
matrix A = [[a, b], [c, d]] and a vector v = [x, y]. Then the linear transformation T(v) = A * v is represented as: T(v) = [[a, b], [c, d]] * [x, y] = [ax + by, cx + dy] This form of representation is not only vital in theory but also incredibly practical in applications, especially when dealing