I'd suggest you draw a coordinate plane: just draw the x- and y-axes. Notice how these axes are PERPENDICULAR to one another.
Now note that the line y = 5 is parallel to the x-axis and x = 2 is parallel to the y-axis. That's all that's necessary for us to claim that x = 2 and y = 5 are perpendicular to each other.
y = (1/8)x and y = 8x - 5 are neither parallel to each other or perpendicular. If their slopes were negative reciprocals, e. g., 8 and -1/8, then the lines would be perpendicular (not true here).
