Trigonometry
posted by Anonymous .
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.

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.
Post your answer for checking if you wish. 
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?