subtraction, fundamental operation of arithmetic; the inverse of addition. If a and b are real numbers (see number), then the number ab 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 ab=a+(−b); e.g., when a=10 and b=5, then 10−5=10+(−5).

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