设圆柱的半径为r，高为h，则πr²h=V，h=V/(πr²)总用料面积为S=2πr²+2πrh=2πr²+2πrV/(πr²)=2πr²+2V/(πr)dS/dr=4πr-2V/(πr²)=0r=(V/(2π))^(1/3)r/h=r/(V/(πr²))=πr³/V=(πV/(2π))/V=1/2
