Given:
The graph of a function.
To find:
The interval at which the graph of the function is a constant.
Solution:
From the given graph it is clear that the graph is a horizontal line and parallel to the x-axis over the interval [tex]1\leq x\leq 6[/tex].
Over the interval [tex]1\leq x\leq 6[/tex], the value of the function is constant, i.e., y=7.
It means the graph of the function is constant over the interval [1,6].
Therefore, the correct option is B.
