A right circular cone is enveloping a right circular cylinder such that the base of the cylinder rests on the base of the cone. If the radius and the height of the cone is 4 cm and 10 cm respectively, then the largest possible curved surface area of the cylinder of radius r is:
Explanation:
Using similarity of triangles,
10-yr = 104
∴ y = 10 - 2.5r
As r is the radius of the cylinder having the largest surface area,
The surface area = 2πrh
= 2πr(10 – 2.5r)
= 5πr(4 – r)
Hence, option (b).
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