A rectangular sheet of iron is 2dm wide and twice as long as it is wide. Cut off the largest semicircle on this iron sheet, what is the area of the cut-off part?
一块长方形的铁皮，宽是2dm，长是宽的2倍．在这块铁皮上截去一个最大的半圆，截去部分的面积是多少平方分米？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<gadget id="calculator">3.14 * 2</gadget>
<output>6.28</output>

<result>6.28</result>