The first figure at the top of the next column is a picture composed of lines and curves. In this exercise we will model only the red semicircle that outlines the top of the silo. In order to make it appear that the person is walking to the right, the background must be translated horizon- tally to the left, as shown in the second figure.

The semicircle at the top of the silo in the first figure is described by f(x) = √9 - x² + 12. 

(a) Graph f in [-12, 12, 1] by [0, 16, 1]. 

(b) To give the illusion that the person is walking to the right at 2 units per second, graph the top of the silo after 1 second and after 4 seconds.