One nice property of round sewer covers is that they cannot fall into the sewer no matter...

One nice property of round sewer covers is that they cannot fall into the sewer no matter how they are oriented. Contrast this with a square, rectangular, or triangular sewer cover. In spite of appearances to the contrary, circles are not the only possible design for sewer covers that cannot fall in. Starting with the equilateral triangle of Figure 4.8 and using arcs of circles, design a sewer cover that is not round but still cannot fall in.

Figure 4.8