
Function Question
I'm currently on chapter 3 of Spivak's Calculus book, which is about functions. I'm confused about what this problem is asking:
Let $\displaystyle f(x)=1/(1+x)$ What is.. $\displaystyle f(x)+f(y)$
I don't understand how you can get an answer when f(y) isn't defined, or anything concerning y for that matter. I'm pretty sure that I'm just thinking about this the wrong way, and would appreciate some help.

Re: Function Question
If $\displaystyle \displaystyle \begin{align*} f(x) = \frac{1}{1 + x} \end{align*}$ and you want to find $\displaystyle \displaystyle \begin{align*} f(y) \end{align*}$, substitute y as x.

Re: Function Question
So unless y or any other variable isn't previously defined, you simply treat it as a number?

Re: Function Question