To make a cylindrical exhaust pipe (without bottom) with a bottom radius of 2 decimeters and a height of 5 meters, at least how many square meters of iron sheet is required.
做一个底面半径为2分米，高为5米的圆柱形排风管(无底)，至少需要多少平方米的铁皮．
<gadget id="calculator">2 / 10</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 * 3.14 * (1/5) * 5</gadget>
<output>6.28</output>

<result>6.28</result>