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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