Usually, we represent losses with negative numbers. Using that representation, a loss of $975 would be represented by the integer -975.
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The additive inverse of this number is also called its "opposite." It is found by changing the sign: additive inverse = +975.
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The sum of a number and its additive inverse is zero. The opposite of a loss is a gain. The value +975 represents the gain (the investment's earnings) that would bring the net change in investment value back to zero.