The radius of the earth's equator is about 6380 km, how many kilometers is a circle around the earth's equator?
地球赤道的半径约是6380km，绕地球赤道一圈约是多少千米？
<gadget id="calculator">2 * 3.14 * 6_380</gadget>
<output>40_066.4</output>

<result>40_066.4</result>