The perimeter of a square is 16 decimeters in 25. How many square decimeters is its area?

The perimeter of a square is 16 decimeters in 25. How many square decimeters is its area?

Square area = (perimeter / 4) ^ 2 = (16 / 25 / 4) ^ 2 = 16 / 625

A man cuts a square sheet of iron into the largest circle. The remaining area is 12.9 square decimeters. Find the area of the circle

Let's take 3.14. If the radius of the circle is r, the square becomes 2R, so the square of 2R minus 3.14 times the square of R, and the multiplication is 12.9, so the square of R is 15, so the area of the circle is 3.14 times 15, which is 47.1