# Math Help - domain question

1. ## domain question

Hey everybody, I just had a quick question about domain and how to write them in interval notation (I think that's what it's called).

So I have one problem,
$
f(x)=\frac {2x-5}{x^2-5x-6}
$

For this problem I got the domain:
$
(-\infty, -1) \cup (-1, 6) \cup (6, \infty)
$

For the other problem,
$
f(x)= \frac {2x-7}{x^2-x-12}
$

with this domain:
$
(-\infty, -3) \cup (4, \infty)
$

My question is this: why are there two 'U' in the first domain but not the second one? Have I just written the second one incorrectly? Any help is appreciated!

2. Originally Posted by sciencefun
in the second domain function,you forgot to include:
(-3,4) as your domain.
Ok I had a feeling I had that second one wrong. So would the middle part always be included in every domain?

3. Originally Posted by kevin11
Ok I had a feeling I had that second one wrong. So would the middle part always be included in every domain?
The domain is all real numbers except for values of x such that x^2 - x - 12 = 0. You should think about why.