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Consider the region bounded by y = x³, x = 2, and y = -1. Rotate the region around y = -1. What is the resulting solid?

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

1 Answer

4 votes

Final answer:

None of the options provided (cone, cylinder, sphere, torus) correctly describe the solid resulting from rotating the region bounded by y = x³, x = 2, and y = -1 around the line y = -1. The nature of the function and the region's bounds preclude these shapes.

Step-by-step explanation:

The student's question refers to the volume generated by rotating a 2-dimensional region around a line (which, in this case, is y = -1) to create a 3-dimensional solid. This process is known in calculus as the method of disks or washers. The original region is bounded by y = x³, x = 2, and y = -1. When this region is rotated around y = -1, each slice perpendicular to the y-axis forms a disk whose radius is determined by the distance from y = -1 up to the curve y = x³. This means the radius of a disk at any given y is x³ - (-1) = x³ + 1. The volume of a solid resulting from such rotation can often form shapes like cylinders, cones, spheres, or toruses, depending on the original 2D region.

However, due to the cubic nature of the function y = x³ and the particular bounds given, the resulting solid is none of the shapes listed. The shape won't be symmetrical on all sides like a sphere or have the regular dimensions of a cylinder or cone. Also, since it does not involve the rotation of a donut-shaped region, it won't form a torus. Thus, none of the given options (1 to 4) correctly describe the resulting solid from rotating the given region around y = -1.

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