On the grass, tie a 5-meter-long rope to a wooden post at one end, and tie a lamb at the other end (not counting the joint). What is the maximum area that the lamb grazes in square meters?
在草地上用一根5米长的绳子一头拴在一个木桩上，另一头拴住小羊(接头处不计)，小羊吃草的范围最大是多少平方米．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>