If the radius of the circle is r=12cm, then the arc length 1= how much cm is the central angle of 18°.
如果圆的半径r=12cm，那么18°的圆心角所对的弧长1=多少cm．
<gadget id="calculator">18 * 3.14 * 12</gadget>
<output>678.24</output>

<gadget id="calculator">678.24 / 180</gadget>
<output>3.768</output>

<result>3.768</result>