Do you think writing +-scalar is considered an acceptable convention? I would like to know whether you think writing the following expression is considered acceptable:
$$ 3x +-9 $$
Do writing $+-9$ as a way to express $+(-9)$ considered acceptable?
I'm thinking about it as writing $+9$, but replacing $9$ with the scalar of $-9$.
It feels odd doing it, because it's using two operators in sequence, but when you think of -9 as a scalar, it feels fine.
Thank you.

If you write $3x+-9$, people will probably know what you are talking about, but this is usually more acceptable:
$$3x+(-9)$$
These parentheses make it more clear that the $-$ is a negative sign on the scalar $-9$ while the $+$ is the operation signifying the addition of the terms $3x$ and $-9$.
