Les nombres relatifs

Les règles

Additions

$( + 4) + ( + 5) = ( + 9)$
$( + 4) + ( - 5) = ( - 1)$
$( - 4) + ( + 5) = ( + 1)$
$( - 4) + ( - 5) = ( - 9)$

Soustractions

$( + 4) - ( + 5) = ( - 1)$
$(+4) - (-5) = (+9) \Rightarrow (-) (-) = (+)$
$( - 4) - ( + 5) = ( - 9)$
$( - 4) - ( - 5) = ( + 1)$

Multiplications

$(+4) \times (+5) = (+20)$
$(+4) \times (-5) = (-20)$
$(-4) \times (+5) = (-20)$
$(-4) \times (-5) = (+20)$

Divisions

$(+4) \div (+2) = (+2)$
$(+4) \div (-2) = (-2)$
$(-4) \div (+2) = (-2)$
$(-4) \div (-2) = (+2)$

Parenthèses

$a + (c + d) = a + c + d$
$a - (c + d) = a - c - d$
$a - (c - d) = a - c + d$
$a - (( - c) + d) = a + c - d$
$a - (( - c) - d) = a + c + d$