Cut out the largest circle from a square paper with an area of 10 square decimeters. What is the area?
从一个面积为10平方分米的正方形纸里剪一个最大的圆，面积是多少．
<gadget id="calculator">3.14 * 2.5</gadget>
<output>7.85</output>

<result>7.85</result>