Radian
01
弧度, 测量角度的单位，定义为圆的半径沿其边缘放置时所形成的角度
a unit for measuring angles, defined by the angle made when the radius of a circle is laid along its edge
例子
An angle of 1 radian means the arc length is the same as the radius of the circle.
1 弧度的角度意味着弧长与圆的半径相同。
Trigonometric functions like sine and cosine often use radians.
像正弦和余弦这样的三角函数经常使用弧度。
