# Trigonometry

Which of the following pairs of vectors are orthogonal?
(i) v = 18i − 3j and w = −i − 6j
(ii) v = 15i − 2j and w = −4i + 30j
(iii) v = 3i − j and w = i + 3j
A. (i) and (ii)
B. (i) and (iii)
C. (ii) only
D. (i) only
17.

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1. Calculate the dot product of the three pairs of vectors. If the dot product is zero, the vectors are orthogonal.
For example,
(i)<18,-3>.<-1,-6>=-18+18=0
So pair (i) is orthogonal.

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2. v•w = 0 if v┴w

18i−3j • −i−6j = 0
15i−2j • −4i+30j = -120
3i−j • i+3j = 0

Can you take it from here?

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