Symbols:Arithmetic and Algebra/Plus or Minus

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Plus or Minus

$\pm$

Plus or minus.

$a \pm b$ means $a + b$ or $a - b$, often seen when expressing the two solutions of a quadratic equation.


Its $\LaTeX$ code is \pm .


Examples

Arbitrary Example $1$

Let $x^2 = 49$.

Then:

$x = \pm 7$

This means that the equation $x^2 = 49$ has $2$ solutions: $x = 7$ and $x = -7$.


Arbitrary Example $2$

Consider the expression $a = b \pm 2$.

This means that $a$ and $b$ are related by $a = b + 2$ or $a = b - 2$.


Also see

Precision

$\pm$

Gives an indication of the precision of an observation.

Let $a$ be a measurement of a physical quantity whose true value is $x$.

Then we say:

$x = a \pm b$

which means that:

Given the observation $a$, it is known that $x$ is between $a - b$ and $a + b$.


The $\LaTeX$ code for \(\pm\) is \pm .


Tolerance

$\pm$

Defines a range in which a number may lie.

$x = a \pm b$ means $a - b \le x \le a + b$.

In the context of engineering, it is known as a tolerance, arising from the idea that any number within $\pm b$ of $a$ is a within a tolerable range of the desired value.


The $\LaTeX$ code for \(\pm\) is \pm .


The despicable political term zero tolerance was supposedly coined as a reflection of the above engineering definition.

It of course takes someone with an actual mathematical or engineering background to understand how poisonously unachievable such an aspiration is.


Sources

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