If the diameter of a circle is 8, what is the area of the circle?
一个圆的直径为8，那么这个圆的面积为多少π
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<result>16</result>