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$\begingroup$

I want to express the sign of $a$ multiplied by $b$ in a formula but do not know how to mathematically express the sign of $a$?

I am not sure but using the plus-minus sign isn't correct, is it?

In latex style I would write:

$\pm a \times b$

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    [Sign function](http://en.wikipedia.org/wiki/Sign_function)2012-12-16

2 Answers 2

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Supposing $a,b\neq 0$, the sign of $ab$ is $\text{sgn}(ab)=\frac{\left|ab\right|}{ab}$ The sign of $a$ is $\text{sgn}(a)=\frac{\left|a\right|}{a}$ and so the [sign of $a$] times $b$ is nothing but $\frac{\left|a\right|}{a}b$

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    ok that's great! thanks for your comments :)2012-12-16
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The correct way to formalize the sign of $a$ multiplied by $b$ is $ \mathrm{sgn} (a) \cdot b.$