The radius of a circle is 3 cm, find its area.
一个圆的半径是3厘米，求它的面积．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<result>28.26</result>