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Geometry Difficulty 3.5 AMC 10/12 Find the answer Italy

Problem:

The perimeter of a rhombus is 32 cm32~\mathrm{cm} and each of the two acute angles measures 3030^\circ. What is the volume of the solid obtained by rotating the rhombus about one of its sides?

Pick one

Solution

Solution:

The answer is (B). We observe that the solid of revolution obtained by rotating a rhombus about one of its sides can be seen as a cone superimposed on a "hollowed-out" cylinder. The region of space that is hollowed out of the cylinder is equal to the cone above it, consequently the required volume VV is equivalent to the volume of a cylinder having as height the side of the rhombus (8 cm)(8~\mathrm{cm}) and as radius the height of the rhombus (half the side, that is 4 cm4~\mathrm{cm}). The calculation then gives V=π428=128πV=\pi \cdot 4^{2} \cdot 8=128 \pi

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Source: MathNet, licensed CC-BY-4.0. Statement translated into English from it; metadata (topic, difficulty) added by this project.