## anonymous 4 years ago Hi, how do I express the set R− in interval notation? I know R is the set of all real numbers, but what is R− ?

1. anonymous

all negative real numbers

2. anonymous

Oh, so R is only all *positive* real numbers?

3. anonymous

So in interval notation, it would be (-inf, 0) ?

4. anonymous

(-inf,0)

5. JamesJ

The interval you've written is correct. $\mathbb{R}$ however is all real numbers: positive, negative and zero.

6. anonymous

if it's just R then it's all numbers if it's R+ then positive, R- negative

7. JamesJ

$\mathbb{R}^+ = (0, \infty)$ $\mathbb{R}^+ = (-\infty, 0)$ $\mathbb{R}_{\geq 0} = [0, \infty)$

8. JamesJ

*correction (sorry!) $\mathbb{R}^- = (-\infty, 0)$

9. anonymous

thanks tomas and jamesj, it makes sense now