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Plus or Minus

The symbol $\pm$ is used to denote a quantity which should be both added and subtracted, as in $a\pm b$. The symbol can be used to denote a range of uncertainty, or to denote a pair of quantities, such as the roots given by the Quadratic Formula

x_\pm={-b\pm\sqrt{b^2-4ac}\over 2a}.

When order is relevant, the symbol $a\mp b$ is also used, so an expression of the form $x\pm y\mp z$ is interpreted as $x+y-z$ or $x-y+z$. In contrast, the expression $x\pm y\pm z$ is interpreted to mean the set of four quantities $x+y+z$, $x-y+z$, $x+y-z$, and $x-y-z$.

See also Minus, Minus Sign, Plus, Plus Sign, Sign

© 1996-9 Eric W. Weisstein