maths plse help me..
posted by Anamika on .
Prove that the radius of the base of right circular cylinder of greatest curved surface area which can be inscribed in a given cone is half that of the cone

Hmm. If the cone has radius R and height H, and the cylinder has radius r and height h,
by similar triangles, r/R = (Hh)/H
area of cylinder
a = 2pi r h
= 2pi (R/H) h(Hh)
da/dh = 2pi (R/H) (H2h)
max a when H = 2h
or, if you don't have calculus to help you, let's pick up here:
a = 2pi (R/H) h(Hh)
= 2pi (R/H) (Hh  h^2)
this is a parabola with vertex (maximum value) when h = H/2