Constant Function
A constant function is a linear function for which the range does not change no matter which member of the domain is used. 
for any x1 and x2 in the domain.
With a constant function, for any two points in the interval, a change in x results in a zero change in f(x).
Example:
Graph the function f(x) = 3.
The graph of a constant function is always a horizontal line.
