MathDB
Reflecting a figure to cover the plane

Source: Serbia TST 2024, P6

May 18, 2024
combinatorics

Problem Statement

In the plane, there is a figure in the form of an LL-tromino, which is composed of 33 unit squares, which we will denote by Φ0\Phi_0. On every move, we choose an arbitrary straight line in the plane and using it we construct a new figure. The Φn\Phi_n, obtained in the nn-th move, is obtained as the union of the figure Φn1\Phi_{n-1} and its axial reflection with respect to the chosen line. Also, for the move to be valid, it is necessary that the surface of the newly obtained piece to be twice as large as the previous one. Is it possible to cover the whole plane in that process?