math question regarding domains of two functions..URGENT

[mAdD INDIAN]

Ok say I have function f(x) and g(x).

How would I go about finding the domain of f(x) + g(x)? I don't think I could add up the two functions (both are pretty obscure)..so what would I do?

Thanks a lot!

 

[mAdD INDIAN]

bump!

 

[aux]

answer: the intersection of the domain of f(x) and the domain of g(x)

this is because f(x) + g(x) should be defined on that domain, meaning that *both* f(x) and g(x) should be defined there; thus the intersection


> I don't think I could add up the two functions

adding up the functions has something to do with their ranges (the sets of values they take) and not with their domains so it seems that you need to read the definition of a domain again (don't ask why... would be long explaination, just do it)

good luck !

 

[aux]

<-- me thinks that he should start charging money for answering questions like this

 

[dOrKuS]

Actually aux, shouldn't it be the union of their two domains respectively, and not the intersection.

Brian

 

[dOrKuS]

also, the range is the output, the domain is the values they take.

 

[mAdD INDIAN]

thanks. I figured as much..but got confused over something.

however the two functions i have both have two variables. One has x, and b..while the otehr has x, and a.

now i'm not sure if u consider a & b as constants..because the next question asks: for the domain chosen, find values for a,b where f(x) + g(x) are continuos.

 

[mAdD INDIAN]

Originally posted by: dOrKuS
Actually aux, shouldn't it be the union of their two domains respectively, and not the intersection.

Brian

shouldn't it be the intersection? what if the values of domain for g(x) don't work in f(x)?

 

[dOrKuS]

Sorry, you're right, the intersection.

I was thinking to slowly for my typing

 

[Martin]

Let me make a wild guess....you have a Calculus quiz...tomorrow...4:10-5:00pm

am I right?

 

[aux]

Originally posted by: dOrKuS
also, the range is the output, the domain is the values they take.

nope

Originally posted by: dOrKuS

Actually aux, shouldn't it be the union of their two domains respectively, and not the intersection.

Brian

it's the intersection
example:
f(x) = sqrt (x-1) has domain x>=1 (i.e. x-1>=0)
g(x) = sqrt (2-x) has domain x<=2 (i.e. 2-x>=0)
in order f(x) + g(x) to be defined both square roots should be defined i.e. x should be both >=1 and <=2; i.e. x belongs to [1; 2]
if it was the union (which is the real line f(x) + g(x) would be defined for all values of x, which is not true; for example f(x) + g(x) is not defined for x = -100)


correction:
(i.e. 2-x<=0)
fixed to
(i.e. 2-x>=0)
/me is too tired

 

[mAdD INDIAN]

Originally posted by: MartyTheManiak
Let me make a wild guess....you have a Calculus quiz...tomorrow...4:10-5:00pm

am I right?

holy crap! how did you know? ARE YOU STALKING ME?? ARE YOU?? hehe...i'll be really scared if you tell me what room/building it is in.

 

[dOrKuS]

Quote

--------------------------------------------------------------------------------
Originally posted by: dOrKuS
also, the range is the output, the domain is the values they take.
--------------------------------------------------------------------------------



nope
--------------------------------------------------------------------------------

C'mon aux, I admitted I was wrong, so can you

The domain of a function is the set of all acceptable inputs.

 

[aux]

Originally posted by: dOrKuS
Quote

--------------------------------------------------------------------------------
Originally posted by: dOrKuS
also, the range is the output, the domain is the values they take.
--------------------------------------------------------------------------------



nope
--------------------------------------------------------------------------------

C'mon aux, I admitted I was wrong, so can you

The domain of a function is the set of all acceptable inputs.

sorry, dOrKuS I was typing when you've posted that so I didn't see your post till after I posted mine

 

[Martin]

Originally posted by: mAdD INDIAN

Originally posted by: MartyTheManiak
Let me make a wild guess....you have a Calculus quiz...tomorrow...4:10-5:00pm

am I right?

holy crap! how did you know? ARE YOU STALKING ME?? ARE YOU?? hehe...i'll be really scared if you tell me what room/building it is in.

I knew it!

Your question sounded eeriely familiar, since it was on the second page of my calculus quiz (which I had monday @ 9). Since I you're in Toronto and know half the tutorials are mon @ 9 and the other half tomorrow at 4..I figured you're in the lec 02 or 04 sections.

So what program you in? Taking the 190s or 180s?

 

[mAdD INDIAN]

Originally posted by: MartyTheManiak

Originally posted by: mAdD INDIAN

Originally posted by: MartyTheManiak
Let me make a wild guess....you have a Calculus quiz...tomorrow...4:10-5:00pm

am I right?

holy crap! how did you know? ARE YOU STALKING ME?? ARE YOU?? hehe...i'll be really scared if you tell me what room/building it is in.

I knew it!

Your question sounded eeriely familiar, since it was on the second page of my calculus quiz (which I had monday @ 9). Since I you're in Toronto and know half the tutorials are mon @ 9 and the other half tomorrow at 4..I figured you're in the lec 02 or 04 sections.

So what program you in? Taking the 190s or 180s?

YTeah it is from the quiz you took. Someone told me that question and I was trying to solve it. I'm in the 190s..hence I'm studying for the quiz I have tomrorwo...I need some serious help with that..how did you do? I"m in Comp Eng.

 

[mAdD INDIAN]

wiat...how'd u know i goto UofT?