In mathematics, the additive inverse of a number a is the number that, when added to a yields zero. This operation is also known as the opposite (number), sign change, and negation. For a real number, it reverses its sign: the opposite of a positive number is negative, and the opposite to a negative number is positive. Zero is the additive inverse of itself.
The additive inverse of a is denoted by unary minus: −a (see the discussion below). For example, the additive inverse of 7 is −7, because 7 + (−7) = 0, and the additive inverse of −0.3 is 0.3, because −0.3 + 0.3 = 0 .
The additive inverse is defined as its inverse element under the binary operation of addition (see the discussion below), which allows a broad generalization to mathematical objects other than numbers. As for any inverse operation, the double additive inverse has no effect: −(−x) = x.