Draw the largest circle in the square. The area of the square is 20cm**2. What is the area of the circle?
正方形中画一个最大的圆，正方形面积是20cm**2，圆的面积是多少？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>