A square of grass, with a side length of 4 meters, has a tree at each of the two vertices of the diagonal line, and a sheep is tied to each tree, and the rope is 4 meters long. What is the area of grass that two sheep can eat
一块正方形的草地，边长4米，一对角线的两个顶点各有一棵树，树上各拴一只羊，绳长4米．两只羊都能吃到的草的面积是多少平方米
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">3.14 * 8</gadget>
<output>25.12</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">25.12 - 16</gadget>
<output>9.12</output>

<result>9.12</result>