Cut the largest circle out of a semicircle with a diameter of 8 cm. What is the area of this circle in square centimeters?
在一个直径是8cm的半圆内剪下一个最大的圆，这个圆的面积是多少平方厘米？
<gadget id="calculator">8 / 2 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>