Six lenses in air are shown in Fig. 34.32. Each lens is made of a material with index of refraction n > 1. Considering each lens individually, imagine that light enters the lens from the left. Show that the three lenses shown in Fig. 34.32a have positive focal lengths and hence are converging lenses. In addition, show that the three lenses in Fig. 34.32b have negative focal lengths and hence are diverging lenses.