What is the arc length of a circle with a diameter of 9 cm and a central angle of 40°?
直径为9cm的圆，圆心角40°的弧长是多少？
<gadget id="calculator">40 * 3.14 * 9</gadget>
<output>1_130.4</output>

<gadget id="calculator">1_130.4 / 360</gadget>
<output>3.14</output>

<result>3.14</result>