The area of a square is 18, and the largest circle is drawn inside, what is the area of the circle?
一个正方形的面积为18，里面画一个最大的圆，圆面积为多少．
<gadget id="calculator">18 / 4</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">3.14 * (9/2)</gadget>
<output>14.13</output>

<result>14.13</result>