The winning rule of billiards is to drive the billiard ball on the table into
the designated holes. We try to study the trajectory of the billiard ball, so
that we can predict the direction of the ball. For rational slopes, we got
cutting sequence by setting up the square torus. We simplified cutting sequence
using shearing and flipping and we obtain the transformation between trajectory
slope and cutting sequence. For irrational slopes, we look at some properties
of Sturmian sequence, which help us distinguish between cutting sequence and
Sturmian sequence. In conclusion, in the case of different slopes, we use
different sequences to do research.Comment: 29 pages,11 figures. arXiv admin note: text overlap with
arXiv:1507.02571 by other author