Question

answer 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.

Answer 2

the straight horizontal line denotes that the slope of graph is 0 at the beginning and end of graph. also it denotes the value at corresponding to

$\infty \: and \: - \infty$

if they are in the domain.

hope this helps