Once upon a time, there was a king who knew mathematics. While rewarding his ministers, he wanted to test who was the cleverest. So he said, "Everyone is a meritorious minister. Today, the king will reward everyone and give you an equal long rope. You can surround it as much as you want, as long as the land enclosed is yours, and there is a special reward for the most land. " Ministers formed squares, rectangles, triangles and circles ... When the king saw it, he called the ministers in a circle and gave him a big bag of gold. The other ministers are all confused, just don't know why. Smart students, do you know why?

Tip: Suppose the length of this rope, and then use it as the circumference to calculate the area of the figure respectively, and you will certainly understand.