The arc length of the expanded graph is π r.
Arc length of expanded graph = perimeter of bottom surface
The bottom radius is 1/2r.
Pythagorean Theorem: (1/2r)? +(3√3)? = r?
The solution is r=6, 1/2r=3.
Side area =πrl=3*6*π= 18π.
Liu Jianhui was the greatest mathematician in Wei and Jin Dynasties. He made great contribut