A square vegetable field with a side length of 4 meters, a tree at each of the two vertices of the diagonal line, a sheep tied to each of the two trees, and a rope length of 4 meters, what is the area of the grass that can be eaten by two sheep? How many square meters.
一块正方形的菜地，边长4米，一对角线的两个顶点各有一颗树，两树上各栓一只羊，绳长4米，问两只羊都能吃到草地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>