A line of reflection does not have to be the x- or y-axis. Draw the graph of a function and then draw its image when reflected across several different horizontal or vertical lines. Write the equation of each image. Try this with several different functions. In general, if the graph of y = f (x) is reflected across the vertical line x = a, what is the equation of the image? If the graph of y = f (x) is reflected across the horizontal line y = b, what is the equation of the image?