For a cylinder, if the radius of the base is doubled, and the height is reduced to twice the original size, the volume of the cylinder will be equal to that many times.
一个圆柱，底面半径扩大到原来的2倍，高缩小到原来的2倍，圆柱的体积就多少倍．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>2</result>