NDA
Mathematics
Three Dimensional Geometry
2025
NDA 2025 (Phase 2)
NDA Mathematics Question (2025) — Solution
Question
For the following two (02) items: A plane P is parallel to the line having direction ratios 1, 3, 2 and contains the line of intersection of the planes 6x + 4y - 5z = 2 and x - 2y + 3z = 0. Which of the following are the direction ratios of the line of intersection of the given planes?
Options
- A. 2, 23, 16
- B. 2, -23, -16
- C. 2, 3, 2
- D. -1, 3, -2
Step-by-step solution
The normal vectors of the given planes are n _1 = 6, 4, -5 and n _2 = 1, -2, 3 . The direction vector d of the line of intersection of the planes is given by the cross product of their normal vectors: d = n _1 n _2 = vmatrix i & j & k \\ 6 & 4 & -5 \\ 1 & -2 & 3 vmatrix d = i (12 - 10) - j (18 + 5) + k (-12 - 4) d = 2 i - 23 j - 16 k The direction ratios of the line of intersection are 2, -23, -16 . Answer: 2, -23, -16
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