CBSE Class 12 Mathematics 2026 Main Paper 65/3/3 · Q252 Marksdot_products
CBSE Class 12 Mathematics 2026 Main Paper 65/3/3 · Question 25 (Vector Algebra)
Unit vectors a,b satisfy |a+2b|=|2a−b|. Find their angle.
✅ Step-by-Step Solution
Final Answer: π/2.
- Square both magnitudes and expand using the dot product.
- Using unit norms gives 5+4a·b=5−4a·b, so a·b=0.
- The two unit vectors are perpendicular, giving π/2.
📋 CBSE Stepwise Marking Scheme
- [0.5 marks] Square both magnitudes and expand using the dot product.
- [1 mark] Using unit norms gives 5+4a·b=5−4a·b, so a·b=0.
- [0.5 marks] The two unit vectors are perpendicular, giving π/2.
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