What is the length of an arc with a radius of 5 cm and a central angle of 72°?
半径为5cm，圆心角为72°的弧长是多少？
<gadget id="calculator">72 * 3.14 * 5</gadget>
<output>1_130.4</output>

<gadget id="calculator">1_130.4 / 180</gadget>
<output>6.28</output>

<result>6.28</result>