When calculating the volume of composite shapes, you typically do not subtract the "hidden face" or surface area. Instead, you add the volumes of the individual shapes that make up the composite shape.
Here are some key points to remember:
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Additive Volume: If the composite shape consists of distinct solid parts (like a cylinder on top of a rectangular prism), you should find the volume of each part and then sum them up.
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Removing Overlaps: If there are overlapping parts or if one shape is "cut out" from another (like a cylindrical hole in a block), you will need to subtract the volume of the removed section from the total volume.
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Surface Areas: The calculation of surface area is different from volume. If you need to find the surface area of a composite shape, you may need to consider the hidden or internal surfaces, especially if one shape is within another since they will not be exposed on the outer surface.
In summary, for volume, simply sum the volumes of all individual shapes unless you are removing a part from the total volume because it is not a part of the composite shape.