Home › CBSE Class 12 › Mathematics › Surface Areas and Volumes › The angle between the lines with direction ratio…
The 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: NCERT Class 12 Maths Part 2 Ch 11 "Three Dimensional Geometry", §11.4_
Related questions
Painting the outside of a toy needs to be worked out from its:Breaking a hard problem into solved smaller ones is the method:A cylindrical tube with a rounded end is a cylinder with a:Pouring a liquid into a container of another shape keeps its:Joining two solids at their flat faces hides those faces:Which solid is not among the basic ones met earlier?The word frustum comes from Latin, meaning a piece:The two circular ends of a frustum have radii that are: