This is a question to test your abstract thinking, mainly by using symmetrical relations. Since the reflection angle is equal to the incident angle when it bounces, you can expand the whole square space of 1* 1 into a plane composed of 1* 1
As shown in the figure, to establish a coordinate system, we might as well take the upper left corner of the first small square as the far point, and the linear equation is y=-3/4x+3/7.
When x=m+3/7? And y=2*n (m, n is an integer, and the 2 before n determines whether to return to AB side or CD side, which is somewhat abstract), which is equivalent to the moving point P returning to E.
The rest is the solution, at this time x=4/7-4/3y, that is.
m+3/7=4/7-4/3*2n
that is
n=(3- 14)m/2 1
Just find the smallest m and make n an integer, and do the math yourself.
Then, the number of collisions between p and the square edge is this straight line. Before the end, just count the number of collisions with the grid.
No matter what other initial conditions are changed to the topic, this calculation can be done!
It's a little abstract, please think it over. I know very well that it is still troublesome to say it.