# 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 $x(x-18)>0$.
Originally Posted by sadieann
I know that..but i need the domain in interval notation of that function
Well, if you know this is the case, then for what values of x is this inequality true? Just solve the inequality. Its fairly straightforward. Once you solve the inequality, the intervals become pretty obvious.

--Chris

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 $x(x-18)\geq 0$."

6. Thank you so much man.

7. A pleasure to help. I understand you were in a rush but when you have time, try to understand what I did and ask us if you don't understand. Good luck.