alleryTwo vectors are PARALLEL (or anti-parallel) iff:
Aā × b̄ = 0
Bā · b̄ = 0
Cā + b̄ = 0
D|ā|² = |b̄|²
Answer & Solution
Correct answer: A. ā × b̄ = 0
Cross product magnitude is |ā||b̄|sin θ.
For parallel (θ = 0) or anti-parallel (θ = 180°), sin θ = 0, so ā × b̄ = 0.
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