What is the area of a circle with a radius of 2 cm in square centimeters?
半径是2厘米的圆的面积是多少平方厘米．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>12.56</result>