level4 unite1 part 2 learning

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。