Let w = î + ĵ − 2k̂, and u and v be two vectors such that u × v = w and v × w = u. Let α, β, γ, and t be real numbers such that
u = αî + βĵ + γk̂, −tα + β + γ = 0, α − tβ + γ = 0, and α + β − tγ = 0.
Match each entry in List-I to the correct entry in List-II and choose the correct option.
| List-I | List-II |
|---|---|
| (P) |v|² is equal to | (1) 0 |
| (Q) If α = √3, then γ² is equal to | (2) 1 |
| (R) If α = √3, then (β + γ)² is equal to | (3) 2 |
| (S) If α = √2, then t + 3 is equal to | (4) 3 |
| (5) 5 |
Correct Answer :
(P) → (2), (Q) → (1), (R) → (4), (S) → (5)
Solution :
The correct option is (P) → (2), (Q) → (1), (R) → (4), (S) → (5).
Given:
And two vectors and satisfy:
1)
2)
From equation (1), is perpendicular to both and . Therefore, the angle between and is 90°.
Taking the magnitude of equation (1):
Similarly, from equation (2), since is perpendicular to , taking the magnitude gives:
Substituting into the first magnitude equation:
Since , we have:
This matches (P) → (2).
Next, the magnitude of is:
Thus, the magnitude of is:
Since , we have:
We are given a system of homogeneous linear equations in :
For a non-trivial solution (since ), the determinant of the coefficient matrix must be zero:
Expanding this determinant:
Factoring this cubic equation gives:
Thus, the possible values of are or .
Case 1: If
Substituting into the system of equations gives:
Since , we have:
Thus, if , then .
Therefore, .
This matches (S) → (5).
Case 2: If
Substituting into the system equations, they all simplify to:
If , then:
Squaring both sides:
This matches (R) → (4).
Additionally, since and are perpendicular, their dot product is zero:
Subtracting this from :
Thus, .
This matches (Q) → (1).
Access expert-curated educational resources and study materials—completely free.
Create, conduct, and manage professional online assessments with Mindyard. Perfect for teachers and institutes.
Copyright © 2026 Mindyard. All Rights Reserved.