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Example

Evaluating x-x for Given Values of xx

To evaluate the expression x-x, substitute the given value for xx and then determine the opposite of that value.

When x=8x = 8: Replace xx with 88 to obtain (8)-(8). The opposite of 88 is 8-8, so x=8-x = -8.

When x=8x = -8: Replace xx with 8-8 to obtain (8)-(-8). The opposite of 8-8 is 88, so x=8-x = 8.

This example illustrates a key point: without knowing whether a variable represents a positive or negative number, we cannot determine the sign of x-x. If xx is positive, then x-x is negative; if xx is negative, then x-x is positive.

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Updated 2026-04-21

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