1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Short easy question, what does this sort of plus minus symbol mean?

  1. Oct 3, 2011 #1
    I'm studying for a quantum exam and there is this symbol that looks like an inverted plus minus but the minus is attached to the plus...
    kind of like

    + but attached.
    in context:

    "x ± vt = constant or x = (-/+) + constant."

    Thanks for any speedy help!
  2. jcsd
  3. Oct 3, 2011 #2
    Found an answer on wikipedia:

    There is another character, the minus-plus sign (∓) which is seen less often. It is generally used in conjunction with the "±" sign, in such expressions as "x ± y ∓ z", which can be interpreted as meaning "x + y − z" or/and "x − y + z", but not "x + y + z" nor "x − y − z". The upper "−" in "∓" is considered to be associated to the "+" of "±" (and similarly for the two lower symbols) even though there is no visual indication of the dependency.
    Thanks anyways.
  4. Oct 3, 2011 #3
    isn't this introductory mathematics? :) when solving a quadratic equation you get this plus-minus sign all the time.
  5. Oct 3, 2011 #4
    A good example of the use of the minus plus symbol is the following trig identity:

  6. Oct 3, 2011 #5
    ah that came out pretty small... if you click it, it gets much larger!
  7. Oct 4, 2011 #6


    User Avatar

    Staff: Mentor

    Larger, yes. But strangely, illegible. It shows as the negative of the photo, here. Oh, well then, I guess I'll just never know. :cry: :cry:
  8. Oct 4, 2011 #7
    How odd! I'll write it here then:

    [itex]cos(\alpha ± \beta) = cos \alpha cos \beta \mp sin \alpha sin \beta [/itex]

    All it's saying is that when you use the plus on the LHS, you use the minus on the right and vice-versa.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook