subtraction, fundamental operation of arithmetic; the inverse of addition. If a and b are real numbers (see number ), then the number a b is that number (called the difference) which when added to b (the subtractor) equals a (the subtrahend). In terms of addition the symbol − b is called the additive inverse of b with the property that the sum of a number and its inverse equals 0, or b +(− b )=0. It follows that −(− b )= b. The subtraction of b from a is the same as the addition of a and the inverse of b, or a b = a +(− b ); e.g., when a =10 and b =5, then 10−5=10+(−5).

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