A cylindrical cistern has a bottom radius of 2 meters and a height of 6 meters. If the water level is lowered by 0.5 meters, how many cubic meters need to be drained?
一个圆柱形蓄水池，底面半径是2米，高是6米，要是水面降低0.5米，需要排水多少立方米？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4 * 0.5</gadget>
<output>6.28</output>

<result>6.28</result>