# Short easy question, what does this sort of plus minus symbol mean?

1. Oct 3, 2011

### aschulz90

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. Oct 3, 2011

### aschulz90

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.

3. Oct 3, 2011

### Cipherflak

isn't this introductory mathematics? :) when solving a quadratic equation you get this plus-minus sign all the time.

4. Oct 3, 2011

### davo789

A good example of the use of the minus plus symbol is the following trig identity:

5. Oct 3, 2011

### davo789

ah that came out pretty small... if you click it, it gets much larger!

6. Oct 4, 2011

### 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.

7. Oct 4, 2011

### davo789

How odd! I'll write it here then:

$cos(\alpha ± \beta) = cos \alpha cos \beta \mp sin \alpha sin \beta$

All it's saying is that when you use the plus on the LHS, you use the minus on the right and vice-versa.