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Two non-zero vectors a and b are PERPENDICULAR if and only if:
A$a + b = 0$ (zero sum)
B$a × b = 0$ (zero cross)
C$a · b = 0$ (zero dot product)
D$|a| = |b|$ (equal magnitude)
Answer & Solution
Correct answer: C. $a · b = 0$ (zero dot product)
PERPENDICULAR vectors have dot product = |a||b| cos 90° = 0. So a · b = 0. CROSS PRODUCT = 0 means PARALLEL vectors.
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