Tutu is a good boy who herds sheep. He leads a sheep to the lawn. Tethered to a tree stump. At this time, he suddenly thought of the knowledge about the circle he had learned, and measured the length of the sheep-leading rope to be 3 meters. What is the maximum area that the sheep grazes?
图图是个放羊的好孩子，他把一头羊牵到草坪上．拴在树桩上．这时，他突然想到所学的圆的相关知识，就测量出牵羊绳长3米，这头羊吃草的最大面积是多少．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<result>28.26</result>