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Let r be the region enclosed by y = x⁴, x = 2, and y = 0 rotated about the y-axis. What is the resulting solid?

1) A cone
2) A cylinder
3) A sphere
4) A torus

1 Answer

4 votes

Final answer:

The solid of revolution formed by rotating the region bounded by y = x⁴, x = 2, and y = 0 around the y-axis does not perfectly match any standard geometrical figure but is closest to a torus, which is not entirely accurate. The volume of a sphere is ⅓πr³, which is distinct from the surface area, 4πr².

Step-by-step explanation:

The student is inquiring about the resulting solid of a region enclosed by certain equations, which is then rotated around the y-axis. To clarify, when a region bounded by the curve y = x⁴, the line x = 2, and the x-axis (y = 0) is rotated about the y-axis, it creates a three-dimensional solid known as a solid of revolution. In this case, the resulting figure is not a cone, a cylinder, or a sphere; instead, the shape starts as a point at the origin and widens as it extends outwards, forming a curved, bell-shaped object that is neither of the given standard geometrical figures. Therefore, based on the options provided, the closest description, although not entirely accurate, would be a torus, even though a genuine torus would require the revolution of a circular area rather than a power function like x⁴.

The volume of a sphere, for reference, is given by the formula ⅓π, not 4². The former expression relates to the volume, while 4π represents the surface area of a sphere. This distinction is crucial when studying geometric properties such as volume and surface area.

User Dan Gerhardsson
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