Cube from space diagonal: The space diagonal of a cube is 8√3 cm. Find the total surface area of the cube (in cm2).
Aptitude
Volume and Surface Area
Difficulty: Easy
Choose an option
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A512 cm2
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B384 cm2
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C192 cm2
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D786 cm2
Answer
Correct Answer: 384 cm2
Explanation
Introduction / Context:The problem links a cube’s space diagonal to its edge length and then asks for surface area. This is a direct application of the cube diagonal relation and the surface area formula.
Given Data / Assumptions:
- Space diagonal d = 8√3 cm
- For a cube of edge a: d = a√3
Concept / Approach:
- Compute a from d = a√3.
- Surface area SA = 6 * a^2.
Step-by-Step Solution:
Given d = 8√3 and d = a√3 ⇒ a = 8.SA = 6 * a^2 = 6 * 8^2 = 6 * 64 = 384 cm2.Verification / Alternative check:
Recompute: a = d / √3 = (8√3)/√3 = 8; SA = 6*64 = 384.Why Other Options Are Wrong:
- 512 cm2: Uses 8 faces or wrong formula.
- 192 cm2: Halves the correct value.
- 786 cm2: Arbitrary, not from standard formula.
Common Pitfalls:
- Confusing space diagonal with face diagonal (face diagonal = a√2).
- Forgetting to square a when computing SA.
Final Answer:
384 cm2