Polyhedra and Prisms — Worked Examples

These examples move from topological checks to direct and inverse prism calculations. Keep base geometry separate from the perpendicular distance between the parallel base planes.

Example 1: Verify Euler's formula for a cube

A cube has 88 vertices, 1212 edges, and 66 faces. Verify Euler's formula.

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Example 2: Recover an unknown face count using Euler's formula

A convex polyhedron has V=10V=10 vertices and E=15E=15 edges. Determine the number of faces.

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Example 3: Volume and total area of a rectangular prism

A closed rectangular prism measures 4.00 m×3.00 m×5.00 m4.00\,\text{m}\times3.00\,\text{m}\times5.00\,\text{m}. Determine its volume and total surface area.

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Example 4: Right-triangular prism

A right-triangular prism has base legs 3.00 m3.00\,\text{m} and 4.00 m4.00\,\text{m} and prism height 10.0 m10.0\,\text{m}. Determine its volume and total surface area.

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Example 5: Oblique prism volume uses perpendicular height

An oblique prism has base area 18.0 m218.0\,\text{m}^2, perpendicular height 7.00 m7.00\,\text{m}, and lateral edges 8.50 m8.50\,\text{m} long. Determine its volume.

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Example 6: Inverse prism height from prescribed volume

A prism has constant base area B=12.5 m2B=12.5\,\text{m}^2 and must enclose 100 m3100\,\text{m}^3. Determine the required perpendicular height.

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Example 7: Cube volume and area

A concrete cube has side length 5.00 m5.00\,\text{m}. Determine its volume and total surface area.

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Example 8: Cube side from total surface area

A cube has total surface area 294 cm2294\,\text{cm}^2. Determine its side length and volume.

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Example 9: Scaling a cube

A cube side is doubled. Determine the factors by which its total surface area and volume change.

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Example 10: Truncated triangular prism from vertex heights

A triangular base has area B=24.0 m2B=24.0\,\text{m}^2. A plane cuts a right prism so the three heights measured at the base vertices are 4.004.00, 6.006.00, and 8.00 m8.00\,\text{m}. Determine the volume when the cutting-plane height varies linearly over the triangular base.

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Example 11: Material mass from prism volume

A rectangular concrete block is 1.20 m×0.800 m×0.500 m1.20\,\text{m}\times0.800\,\text{m}\times0.500\,\text{m}. If concrete density is 2400 kg/m32400\,\text{kg/m}^3, estimate its mass.

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Example 12: Compare two prisms with equal base area

A rectangular prism has base dimensions 6.00 m×2.00 m6.00\,\text{m}\times2.00\,\text{m} and height 5.00 m5.00\,\text{m}. A right-triangular prism has base legs 6.00 m6.00\,\text{m} and 4.00 m4.00\,\text{m} and the same height. Compare their volumes.

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Prism calculation check

For oblique prisms, do not substitute lateral-edge length for perpendicular height. For surface area, verify whether the prism is right or oblique before using PhPh as the lateral area. Topological counts such as VV, EE, and FF are dimensionless and should not be mixed with geometric volume notation without context.