If ā × b̄ = 0 and neither is the zero vector, then:
Aā and b̄ are parallel/anti-parallel
Bā and b̄ are perpendicular
C|ā| = |b̄|
Dā = b̄
Answer & Solution
Correct answer: A. ā and b̄ are parallel/anti-parallel
|ā × b̄| = |ā||b̄|sin θ = 0 with non-zero vectors means sin θ = 0, so θ = 0 or 180° — parallel or anti-parallel (collinear).
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