A cow is tied to a stump by a rope 3 meters long. What is the range of movement of the cow?
一头牛被一根3米长的绳子拴在树桩上，这头牛能活动的范围是多少平方米．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>