The equation y = 4 represents a horizontal line in the Cartesian plane where the value of y is constantly 4 for any value of x. This means that regardless of the x-coordinate, the y-coordinate will always be 4.
To determine if this graph is a function, we can use the definition of a function: a relation where each input (in this case, each x-value) corresponds to exactly one output (the y-value). Since every x-value maps to y = 4, it satisfies the criteria of a function.
Additionally, we can apply the vertical line test. If a vertical line drawn anywhere on the graph intersects the graph at more than one point, it is not a function. In the case of y = 4, any vertical line will intersect the line at exactly one point. Hence, it confirms that y = 4 is indeed a function.