数学吧 关注:849,120贴子:8,600,172
  • 7回复贴,共1

求大神来解答!圆锥问题

只看楼主收藏回复

大概意思是圆锥体的斜边长度固定,求证当圆锥体体积最大时,侧面展开扇形的圆心角是(图中那个数值)。跪求大神解答!


IP属地:湖北来自iPhone客户端1楼2015-02-10 23:18回复
    没人吗


    IP属地:湖北来自iPhone客户端2楼2015-02-10 23:58
    回复
      大学数学题?


      来自iPhone客户端4楼2015-02-11 00:44
      回复
        OK, you are right, the answer should be 2\sqrt{2}/\sqrt{3} π
        Let the cone angle be θ, then the volume is expressed as (π l^3 sin^2 θ cos θ)/3
        Set t=cos θ, then the volume = (π l^3 / 3)(t-t^3), where t∈[-1,1]
        Taking derivative gives t=1/\sqrt{3} should be the maximum point,
        which implies the desired result.


        5楼2015-02-11 00:44
        收起回复
          楼主别水了,存钱买套燕郊 吧 不知道什么是燕郊 ?放心,楼下的龟儿子会给你解释的


          IP属地:河南来自Android客户端6楼2015-02-11 05:09
          收起回复