Question

what could be explained from the straight horizontal line observed at the beginning and end of the graph​

Answer 1

The graph of a relation of the form y = 5 is a line parallel to the x-axis because the y value never changes.  

A line parallel to the x-axis is called a horizontal line.

The graph of a relation of the form x = 5 is a line parallel to the y-axis because the x value never changes.

A line parallel to the y-axis is called a vertical line.