Today, I saw such a problem in the training of Mathematics 1+2. A cubic casting with a bottom area of 648 square centimeters, what is the remaining three-dimensional graphic area after removing the largest cylinder and taking the opposite side as the bottom?

Seeing this topic, I was very confused and thought: just say a bottom area, how to do it? My mother sat in a chair and looked at it. She smiled at me and said, "Hum, it's so advanced that I can't even know this problem."

I know that my mother used the challenge method to provoke my competitive spirit and let me finish the problem. In order to make my mother think that her challenge method was successful, I crustily skin of head and did it, but I couldn't figure it out. But I didn't lose heart. I kept doing it and made it.

According to the drawing (to be drawn), it can be found that when a cylinder is cut off, a hole with the same size as the original cylinder will come out. Although the volume of the hole is the same as that of the cylinder, their surface areas are not the same, but the areas of the two bottoms are smaller than that of the original cylinder.