# Disambiguating minus

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The term minus is represented by the sign $-$. It has two different meanings:

1) Negation (unary minus):

Example: Today the temperature is minus $5$ degrees outside.

2) Subtraction (binary minus):

Example: Yesterday the temperature was minus $5$ degrees, and it has decreased by $3$ degrees since then. Hence, today the temperature is minus $8$ degrees,
which we express in ordinary algebra as $\; -5 \,- \,3 \, = \, -8$.

Note: In the last example, the first minus sign to the left of the $=$ sign represents negation, and so does the minus sign to the right. In contrast, the second minus sign to the left of the $=$ sign represents subtraction.

Using the appropriate form of equality, the temperature example would be more clearly expressed as

$\; \stackrel {\mathrm{neg}}{-} 5 \, \stackrel {\mathrm{sub}}{-} \, 3 \, \equiv \; \stackrel {\mathrm{neg}}{-} 8$.