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Plus sign

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

 


Addition

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

 + + = + 
 + – = –
 – + = –
 – – = +

 


History

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


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