•Given a relation in x and y, we say y is a function of x if for each element x in the domain, there is exactly one value of y in the range. It is a rule of correspondence between two nonempty sets, such that, to each element of the first is called domain, there correspondents one and only one element of the second is called range. Read the details about function notation inTo determine whether it is function by using the vertical line test. If the graph passed to Vertical line test it is consider as function. The graph of function defines y as a function of x if no vertical line intersects the graph in more than one point.