Show that the semi-vertical angle of the cone of the maximum value and of given slant height is tan ^−1√2
Show that the semi-vertical angle of the cone of the maximum value and of given slant height is tan ^−1√2

Let  be the radius,  be the height,  be the slant height of given cone and  be the semi-vertical angle of cone.

  

        ……….(i)

  Volume of the cone (V) =        ……….(ii)

  V = 

  and 

Now 

 

 

 

 

At  

   [Negative]

  V is maximum at 

  From eq. (i), 

 

  Semi-vertical angle,