# Homework Help: A simple question about functions

1. Jul 11, 2009

### potmobius

1. Let f(x) = 1/(1+x). What is:
a. f(1/x)
b. f(x+y)

3. The attempt at a solution
Frankly, I have no idea how to do this. But does the first one mean the inverse of the original function? and for the second one, no value for "y" is specified. So I'm lost...

2. Jul 11, 2009

### Coto

Hi potmobius,

What would you have done if the question instead asked for f(5) or f(0)?

It is no different for these questions. Simply plug in the argument (in this case 1/x and x+y) into where x is.

3. Jul 11, 2009

### Dunkle

How would you find f(1)? Plug in 1 for x. How would you find f(2)? Plug in 2 for x. How would you find f(3)? Plug in 3 for x. So how would you find f(1/x) and f(x+y)?

4. Jul 11, 2009

### potmobius

okay, i think i understand the f(x+y) part... but i still have some doubt about f(1/x). Do i treat the (1/x) part as just another variable, like y, for instance?
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for the f(x+y) part, i did it like this:

f(x+y) = 1/(1+x+y)

is it correct? is that all there is to it?

5. Jul 11, 2009

### potmobius

for f(1/x) i got f(1/x) = x/(x+1)

is that correct?

6. Jul 11, 2009

### Coto

Yes, this is correct potmobius.

7. Jul 11, 2009

### potmobius

Thanks a lot Coto! That really cleared up things!