# Math Help - function compositions

1. ## function compositions

Here's the problem: Find sets $A, B$ and $C$ and functions $f:A\longrightarrow B, g:B\longrightarrow C$ and $h:B\longrightarrow C$ for which $f\circ h=f\circ g$ but $g\not=h$.
It doesn't even have to be real example functions, just a picture would be good. I just can't think of anything. Thank you!

2. Originally Posted by sfitz
Here's the problem: Find sets $A, B$ and $C$ and functions $f:A\longrightarrow B, g:B\longrightarrow C$ and $h:B\longrightarrow C$ for which $f\circ h=f\circ g$ but $g\not=h$.
It doesn't even have to be real example functions, just a picture would be good. I just can't think of anything. Thank you!
how about $A = B = C = \mathbb{R}$. with $f(x) = x^2,~g(x) = x, \mbox{ and }h(x) = -x$

can you find another example?

3. Oh my god, I am so sorry, I typed the problem wrong. I meant $g\circ f$ and $h\circ f$! Can you still help? The part I typed was part a of the problem, and I'm stuck on part b. I'm really sorry.

4. Originally Posted by sfitz
Oh my god, I am so sorry, I typed the problem wrong. I meant $g\circ f$ and $h\circ f$! Can you still help? The part I typed was part a of the problem, and I'm stuck on part b. I'm really sorry.
how about $g(x) = x,~h(x) = f(x) = 1$

try to find another

5. ok, I understand, f must not be onto for it to work, so that there are elements in B that are outside the image of f. thank you!

6. Originally Posted by sfitz
ok, I understand, f must not be onto for it to work, so that there are elements in B that are outside the image of f. thank you!
can you prove that?

just kidding... well, you can if you want to

7. I did prove it! That was the other part of the question, but I couldn't prove it without being able to think of an example

8. Originally Posted by sfitz
I did prove it! That was the other part of the question, but I couldn't prove it without being able to think of an example
oh, ok. that's fine then