Okay so the domain of f(x) (according to my calculations) is that x<9 and x≠0. How do I write this formally?

"x ∈ (-∞, 0) ∪ (0, 9)"

for interval notation, and

"{x ∈ ℝ | x < 9 | x ≠ 0}"

for set notation?

This is a purely notational question, I'm just wondering what's considered "standard" format/aesthetics-wise in the math world. I don't know if I'm supposed to use the "is an element of" symbol in interval notation and I'm not sure about having two "such that" lines in the set notation?

I know I won't get marked down no matter how I write it on a test, but I'm just curious what's the formalest formal way to do it?