Answer 1: The order of the two letters in the vector has actually specified the direction. For example, vector AB and vector -BA are the same. CD-CB is actually CD+BC, and letters with the same letters can be combined together, which is equal to BD. What you think is equal to DB, and the direction is reversed. Answer 2: That's because we only know the direction of B, which is parallel to A, but we don't know the size of B, that is, the film of B doesn't know it, so multiplying the coefficient in front represents a series of vectors parallel to A. As for how much we get, we must solve it according to the known conditions. Answer 3: To tell the truth, I really don't know. Don't worry about this matter, it's not difficult. It's good to be familiar with some problems.