Geometry
A circle is a two dimensional figure with a radius and circumference, which is the distance around the circle.
圆是一个具有半径和周长的二维图形，它是圆周围的距离。
The area of a circle is PI R squared, where R is the radius and PI is the ratio of a circle circumference to its diameter.
圆的面积是PI R平方，R是半径，PI是圆周与直径的比值。
