The radius of the circle is 2cm, then the length of the arc subtended by the central angle of 72° is 1= how many cm.
圆半径为2cm，那么72°的圆心角所对的弧长1=多少cm．
<gadget id="calculator">72 * 3.14 * 2</gadget>
<output>452.16</output>

<gadget id="calculator">452.16 / 180</gadget>
<output>2.512</output>

<result>2.512</result>