The radius of a circle is 4cm, how many square centimeters is its area?

一个圆的半径是4厘米，它的面积是多少平方厘米？

youdao

That is a circle of radius 1. That's the unit circle.

是一个半径为1的圆，那是单位圆。

youdao

So, that's actually a great circle meridian of length, well, I mean, well, the radius is the radius of the sphere.

路程就是个大圆，我的意思是，这个圆的半径是球的半径。

youdao

That means, it can only be rattling around in a circle of radius R.

也就是说它只能,限制在一个半径为 R 的圆上运动

耶鲁公开课 - 基础物理课程节选

So we know it's moving on a circle of radius r.

因此这个质点始终在做半径为 r 的圆周运动

耶鲁公开课 - 基础物理课程节选

Draw a circle around the central city of Mandalay with a radius of just over 700 miles (1, 100km), he writes, and it stretches to the states of West Bengal and Bihar in India, to Yunnan and Sichuan provinces in China, as well as to Tibet, and south to cover most of Laos and Thailand (see map).

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