Evaluate f (x) at K

I assume you mean something like f(x)=1+k equations or something like that, Guest. Correct me if I'm wrong please ;)

 

These are kind of like two variable equations; f(x) usually represents y or another variable.

You can replace the f(x) as another variable, like y=1+k to make it easier.

However, if it is f(k), that means you plug in the value of k given.

For example: f(k)=1+k, k=1. This is the same as f(1)=1+1=2.