题目

Michael Phelps and his U.S. teammates crowned the greatest single Olympic performance on 17th August, 2008 with a win in the 4×100 – meter medley relay. The victory gave Phelps his eighth gold medal of the Beijing Olympics, the most golds ever won by an athlete at one Games. With gold No. 8, Phelps earned a singular place in the Olympic record books. “There is no comparison in the swimming world for what Michael has done,” said Gregg Troy, coach of U.S. swimmer Ryan Lochte, who finished third to Phelps in two races here in Beijing but also won gold alongside him in the 4×200-met如图，某工厂生产的一种无盖冰淇淋纸筒为圆锥形，现一客户订制该圆锥纸筒，并要求该圆锥纸筒的容积为π．设圆锥纸筒底面半径为r，高为h．（1）求出r与h满足的关系式；（2）工厂要求制作该纸筒的材料最省，求最省时hr的值．