In this example, C is a cyclone moving from A to B in 1 day. [br]Let d be the number of days (which can be a fraction). [br]Position of C can be described in terms of d and the coordinates of A and B. [br][br](In the HK DSE curriculum, this corresponds to the formula for internal point of division. More generally, this can be a vector representation of straight line.)[br][br]