A 6.28-meter-long rope is wrapped around a big tree exactly twice. What is the cross-sectional area of the big tree?
一根6.28米长的绳子，恰好围一棵大树绕了2圈，这颗大树的横截面积是多少？
<gadget id="calculator">6.28 / 2</gadget>
<output>3.14</output>

<gadget id="calculator">3.14 / 3.14 / 2</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 ** 2</gadget>
<output>0.25</output>

<gadget id="calculator">3.14 * 0.25</gadget>
<output>0.785</output>

<result>0.785</result>