Math Help - A simple query regarding inequalities

1. A simple query regarding inequalities

I know that $-1\le \sin x\le 1$.

I also know that it is okay to write $-2<\sin x<2$.

But is it okay to write $-2\le \sin x\le 2$, although the equalities are never attained?

2. Re: A simple query regarding inequalities

It is typically bad form to include Domain just for fun, but it sometimes serves a purpose.

$0 \le 1$

It is a matter of validity, not a matter of "okay". Is it valid? Feel free to write it any way you like if it serves some purpose.