To make a ventilating pipe with a bottom radius of 20cm and a length of 80cm, how many cm of iron sheet is needed at least**2.
做一个底面半径是20cm，长是80cm的通风管，至少需要铁皮多少cm**2．
<gadget id="calculator">3.14 * 20 * 2 * 80</gadget>
<output>10_048</output>

<result>10_048</result>