alleryThe angle between the lines with direction ratios (1, 2, 2) and (2, 1, 2) satisfies
Acos⁻¹(4/9)
Bcos⁻¹(8/9)
Ccos⁻¹(6/9)
D90°
Answer & Solution
Correct answer: B. cos⁻¹(8/9)
1. Dot product: 1·2 + 2·1 + 2·2 = 2 + 2 + 4 = 8.
2. Magnitudes: √(1+4+4) = 3 for each direction vector.
3. cos θ = 8 / (3·3) = 8/9.
4. So θ = cos⁻¹(8/9).
_Source: syllabus Maths Part 2 Ch 11 "Three Dimensional Geometry", §11.4_
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