Square geometric shapes - this is an important characteristic of them, are used in science and engineering.
Circle - is the set of points equidistantfrom the same point of the plane, called the center of the circle. The distance from any point on the circumference to the center is called the radius of the circle. Circle - it's part of the plane bounded by a circle.
The area of a circle S can be found from the formula: S = Π- * R²-, where R - radius of the circle, and Π- - pi.
If you know the diameter, not the radius of the circle, we must remember that D = 2R. Then it is easy to see that the area of a circle can be calculated thus: S = Π- * R²- = Π- * (D / 2) ²- = Π- * D²- / 4