Question

Let vector u = (a, b) and vector v = (c, d). If the vectors are located as shown in the graph, then

Answer 1

We have the following vectors:
 u = (a, b)
 v = (c, d)
 We observe that the vectors form an angle of 90 degrees.
 Therefore, the product u.v is equal to zero.
 We have then:
 u.v = (a, b). (c, d) = 0
 u.v = ac + bd = 0
 ac = -bd
 Answer:
 B) ac = -bd