Line Perpendicular to a Plane

On the bookcase above, which is located in my home office, I was able to spot a line perpendicular to a plane. The pink lines represent the plan, or the framing/backboard of the bookcase. The blue lines highlights the line, in this case the shelf, that is perpendicular to a plane. The green box shows that the line is perpendicular to the plane because when line are perpendicular, they form a right angle. Bookcases, or shelves, are used in the food industry to hold dishes and cookware, they can also hold cookbooks