Draw the largest square in a circle. The area of the square is 36cm**2. Draw the largest circle in the square. What is the area of the circle between the big circle and the small circle?
在一个圆中画一个最大的正方形，正方形的面积是36cm**2，在正方形中再画一个最大的圆，大圆与小圆的圆环面积是多少？
<gadget id="calculator">18 - 9</gadget>
<output>9</output>

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

<result>28.26</result>