What is the area of a circular wooden board with a diameter of 8 cm?
一圆形木板，它的直径是8厘米，面积是多少π平方厘米．
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<result>16</result>