Given two points, A and B, there are two vectors: A-->B and A<--B which are parallel but pointing in opposite directions. I remember learning as a kid a word which simply defines the line upon which the vectors lie and another which defines the direction the vectors move along the line, something like "A-->B and A<--B have the same XXX, but opposite YYY." Can anyone fill in these blanks?

  • All I can find is "opposite vector" or "negative vector". Is it something other than that? – Catija Jun 29 '15 at 19:59
  • I expect you would get an answer quicker on math.stackexchange.com – Avon Jun 29 '15 at 20:00
  • @Catija No, I distinctly remember the structure being as given: "A-->B and A<--B have the same XXX, but opposite YYY". – Wasabi Jun 29 '15 at 20:01
  • 2
    Opposite sense. – Colin Fine Jun 29 '15 at 20:10
  • Your title doesn't clearly reflect the content of the body, and I think my answer reflects the title more than the body. Is my answer appropriate, or should I delete it? – Matt Gutting Jun 29 '15 at 20:44

same magnitude and opposite direction


The vectors are called antiparallel:

In a Euclidean space, two directed line segments, often called vectors in applied mathematics, are antiparallel, if they are supported by parallel lines and have opposite directions.

Note: Two antiparallel vectors need not have the same magnitude (i.e. length); they can be of any length.


same axis but opposite direction?

  • Axis? For a vector? Never heard that used in this context. – Drew Jun 29 '15 at 20:37

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