Plus sign

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A plus sign (+) always reminds us of additions and positive numbers. That makes sense, but there is more.

The calculation

5 + 2 = 7

is clear. It gets a little harder with

–7 + 5 = –2

as this results in a negative number. Even a bit more difficult is

5 + (–2) = 3

because here we have to use a well-known rule

+ + = +
+ – = –
– + = –
– – = +

The Welsh mathematician Robert Recorde introduced the plus sign and the equal sign in his book The Whetstone of Witte to English speakers in 1557.