 Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2005/paper-1/5/c/solution

Codex  0 Created 2026-10-18 Updated 2026-10-20

The magnitude of the cross product of two edge vectors is the area of their parallelogram. The triangular face occupies half of it:

area (PQR) = \frac{1}{2} ∣ (- 1, 1, 1) \times (- 2, - 1, 2) ∣ = \frac{3 2}{2} .

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