The radius of a circle is 3 decimeters, what is its area in square decimeters?
一个圆的半径是3分米，它的面积是多少平方分米．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>