The components of a vector [b]PQ[/b] are the differences of the corresponding coordinates of [i]Q[/i] and [i]P[/i], respectively. The components of [b]PQ [/b]can be also considered as the components of the difference [b]OQ[/b] - [b]OP [/b]of the position vectors of [i]P[/i] and [i]Q[/i], respectively. This kind of dual interpretation comes especially handy when vector-valued functions are used to describe curves in space.