I ran across a post today on the SquareCircleZ blog, lamenting the effect of some of the poor choices of notation that we use in Mathematics.
It reminded me of the trouble that I have been having saying that cosine is x/r and then making r=1 to get a unit circle. Now x=cosine and we graph the values as y = cos x (what is x!!!).
One of the commenters makes an interesting suggestion about the use of brackets. If we adopted this idea, we could see the difference between 5(x) and f(x).