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So in general we find the opposite of a number by adding a '-' sign.

We're able to add the '-' sign to negative numbers as well, but I was wondering if this is correct:

Say we'd want to find the opposite of -7;

$$-(-7)$$

Is it true that one finds the opposite by calculating:

$$-1*-7=7$$

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    $\begingroup$ Yes.${}{}{}{}{}$ $\endgroup$ – TheGeekGreek Aug 1 '17 at 10:25
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Yes it's true. If you want to find the opposite just add (or subtract) the number you need to reach 0, in this case +7, and then add (or subtract) +7 again... the result is the opposite. Adding (or subtracting) 2 times itself passing from negative to positive and viceversa is the same of multiplying for -1, where 1 is the neutral number in multiplication.

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Yes, that's true. The absolute value of a number is its distance from $0$. With your example, we see that $-7$ is $7$ away from $0$. If we choose to think that $-7$ is to the left of $0$, then the opposite of $-7$ is $7$ to the right of $0$. That would be $+7$.

The multiplicative identity is $1$. The opposite of the multiplicative identity is $-1$. Ergo multiplying by $-1$ gives the opposite of a number.

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