# Math Help - Whats the domain?????

1. ## Whats the domain?????

2. The domain is all the $x$ that make $x(x-18)>0$.

3. I know that..but i need the domain in interval notation of that function

4. Originally Posted by arbolis
The domain is all the $x$ that make $x(x-18)>0$.
5. Ok. Note that $x(x-18)$ vanishes when x equals 0 or 18. Note also that $y=x(x-18)=x^2-18x$ is an equation of a parabola with a global minimum. That mean that $x(x-18)\geq 0$ when $x \in (-\infty,0]$ U $[18,+\infty,)$, that's your domain.
EDIT: I'm sorry in my first post, it should be "The domain is all the $x$ that make $x(x-18)\geq 0$."