Divide a circle into several small sectors on average, and put together an approximate rectangle. The length of this rectangle is 6.28 decimeters. What is the area of this circle in square decimeters?
把一个圆平均分成若干个小扇形，再拼成一个近似的长方形，这个长方形的长是6.28分米，这个圆的面积是多少平方分米．
<gadget id="calculator">6.28 / 3.14</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>