# Thread: But I am sure this is correct...

1. ## But I am sure this is correct...

I'm taking freshman calculus at my university, and we're currently reviewing math concepts. I am practically done with my latest online assignment, with the exception of a particular domain the webpage keeps telling me is incorrect, even though I feel very confident with my answer (and the graphing calculator provides further evidence).

Here is the culprit:

Function on top, domain at bottom.

I would really appreciate any help with this predicament!

2. Originally Posted by Desperation
I'm taking freshman calculus at my university, and we're currently reviewing math concepts. I am practically done with my latest online assignment, with the exception of a particular domain the webpage keeps telling me is incorrect, even though I feel very confident with my answer (and the graphing calculator provides further evidence).

Here is the culprit:

Function on top, domain at bottom.

I would really appreciate any help with this predicament!
yes, that's right.

make sure you are not making some kind of syntax error, inputing the answer in a way the system doesn't understand. were there any other restrictions on the function?

3. Everything looks right except, it should be "n" instead of "u".

4. Originally Posted by Linnus
Everything looks right except, it should be "n" instead of "u".
"u" is correct. the intersection is empty, and we know the domain is not empty

5. Originally Posted by Jhevon
"u" is correct. the intersection is empty, and we know the domain is not empty
hmm I always thought that "n" basically means "and" and "u" basically means "or". Thanks for the clear up!

6. Originally Posted by Jhevon
yes, that's right.

make sure you are not making some kind of syntax error, inputing the answer in a way the system doesn't understand. were there any other restrictions on the function?
I am very sure I inputted the answer effectively, after having inputted plenty of interval notations into the website.

There is no particular restriction I know of, the question merely asks to find the function of (f/g)(x) and its domain, where f(x)=√(4x+3) and g(x)=(x-6)/x

7. Originally Posted by Linnus
hmm I always thought that "n" basically means "and" and "u" basically means "or". Thanks for the clear up!
yes, in logic

here, we are dealing with sets. "u" means "union" and "n" means "intersection"

8. Originally Posted by Desperation
I am very sure I inputted the answer effectively, after having inputted plenty of interval notations into the website.

There is no particular restriction I know of, the question merely asks to find the function of (f/g)(x) and its domain, where f(x)=√(4x+3) and g(x)=(x-6)/x
oh, well then, that's different. you cannot have any x in the domain of a composition that was not in the domain of either of the functions. note that, for example, x = 0 was not in the domain of g, thus it cannot be in the domain of (f/g)

9. Originally Posted by Jhevon
oh, well then, that's different. you cannot have any x in the domain of a composition that was not in the domain of either of the functions. note that, for example, x = 0 was not in the domain of g, thus it cannot be in the domain of (f/g)
Well, now that's interesting. I was looking suspiciously at that x = 0 but didn't pay much attention to it... I modified the answer and it's now correct!

This was immensely helpful, thank you very much!

10. Originally Posted by Desperation
Well, now that's interesting. I was looking suspiciously at that x = 0 but didn't pay much attention to it... I modified the answer and it's now correct!

This was immensely helpful, thank you very much!
good

of course, "composition" was the wrong word for me to use, since that refers to something specific. what i said is true for compositions as well, but it is true for other kinds of "combinations" like (f + g), (f - g), (f/g) etc, if there is a problem with a point in any one function, there will be a problem in the combination of that function with something else