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Question #40778
The Question
Let be three mutually orthogonal unit vectors in . Let and be sets of points defined as follows: where is the origin. Let be the convex polyhedron whose vertices are all the points in . Find the sum of the squares of the areas of all the faces of .
Options
- A.
1008
- B.
126
- C.
504
- D.
252
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Monster
Ultra-high difficulty questions designed to test your limit, stamina, and deep conceptual understanding.
Concepts Behind This Question
Condition of Collinearity|Dot Product Projection Sign|Direction Cosines constraint
Why This Question Is Tricky
Common Mistakes
The question tests the condition of collinearity using the dot product projection and the critical trap of sign ambiguity.
Students often solve by incorrectly assuming , forgetting the anti-parallel case .
This error causes the solution space to collapse from 6 points (forming a 3D octahedron) to just 3 points, which are incorrectly identified as merely forming a single coplanar triangle.
Consequently, they calculate the area squared of only one face (126) instead of the full polyhedron (1008).
Quick Facts About This Question
Question Information
| Subject | Mathematics |
| Chapter | Straight Lines - Class 11 |
| Concept | Condition of Collinearity |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |