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maths --plse help me..

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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

  • maths --plse help me.. -

    Hmm. If the cone has radius R and height H, and the cylinder has radius r and height h,

    by similar triangles, r/R = (H-h)/H

    area of cylinder
    a = 2pi r h
    = 2pi (R/H) h(H-h)
    da/dh = 2pi (R/H) (H-2h)
    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(H-h)
    = 2pi (R/H) (Hh - h^2)
    this is a parabola with vertex (maximum value) when h = H/2

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