Minus sign

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A minus sign (–) is always immediately associated with subtraction and negative numbers. That is logical, but there is more.

The calculation of

5 – 2 = 3

is clear. It becomes more difficult with

2 – 7 = –3

as now a negative number is created. A bit more complicated is

5 – (–2) = 7

as we must apply the well known rule

+ + = +
+ – = –
– + = –
– – = +

What should we think of

0.5 = 2⁻¹

Here we have no negative values, and yet we use a minus sign. Many people think this is confusing. You could have written a fraction in stead

We see here that numbers with negative exponents are just fractions, for

This is because we work with decimal numbers.

i^–1 = –i

That is only possible because i has no real value.

The minus sign is also used for inverse functions. The notation is

f (x) with the inverse f ^− 1(x)

On calculators we use

sin⁻¹ for the inverse sine
sinh⁻¹ for the inverse hyperbolic sine

and that is very simple.

The German mathematician Johannes Widmann (1460 - 1498) has introduced the plus sign and the minus sign.