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The angle between two planes with normals n₁ and n₂ is given by
Asin θ = n₁ · n₂ / (|n₁||n₂|)
Bcos θ = |n₁| · |n₂|
Ccos θ = n₁ · n₂ / (|n₁||n₂|)
Dtan θ = n₁ × n₂
Answer & Solution
Correct answer: C. cos θ = n₁ · n₂ / (|n₁||n₂|)
1. The angle between two planes equals the angle between their normals.
2. Use the dot-product formula for angle between vectors.
3. cos θ = (n₁ · n₂) / (|n₁| · |n₂|).
4. Distractors confuse sin/cos or replace the dot product with magnitudes.
_Source: NCERT Class 12 Maths Part 2 Ch 11 "Three Dimensional Geometry", §11.8_
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