26) Show that semi-vertical angle of the right circular cone of given surface area and
maximum volume is
Let r, l, and h are the radius, slant height and height of cone respectively
Now,
Now,
we know that
The surface area of the cone (A) =
Now,
Volume of cone(V) =
On differentiate it w.r.t to a and after that
we will get
Now, at
Hence, we can say that is the point if maxima
Hence proved