Draw the largest circle in a rectangle whose length is 10 cm and width is 9 cm. What is the area of this circle?
在长为10厘米，宽为9厘米的长方形中画一个最大的圆，这个圆的面积是多少．
<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">(9/2) ** 2</gadget>
<output>81/4 = around 20.25</output>

<gadget id="calculator">3.14 * (81/4)</gadget>
<output>63.585</output>

<result>63.585</result>