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I am having a bit of trouble with communicating information about functions in English. I know that $f(x)$ is read $f$ of $x$, but how would I use this in a sentence? Say, we have a argument x=5, and I want to express the process of passing this input to the function, would I then say:

  • taking $f$ of 5 gives $f(5) = 5^2+1$,
  • putting the argument $x=5$ gives $f(5) = 5^2+1$ (this seems ambiguous if multiple functions exists), or
  • putting $x=5$ and applying function $f$ gives $f(5) = 5^2+1$?

I suspect that the first option is correct, but English is not my native language and I'd love some feedback on this.

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The first two bullet points should have "gives" instead of "give". The first one would then be fine. It seems you're trying to say something in a slightly unnatural way though, I'd say "when its argument is 5, $f$ takes the value $5^2+1$" or "applying the function $f$ to 5 gives $5^2+1$" or just "$f$ applied to 5 gives $5^2+1$". – m_t_ Jan 2 '13 at 11:51
thank you for the input, much appreciated :) – JustDanyul Jan 2 '13 at 11:59
up vote 4 down vote accepted

Evaluating the function $f$ at the point $x=5$ gives $f(5)=5^2+1$.

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+1. Or "$f$ evaluated at $x=5$ is $f(5)=5^2+1$". – Stefan Hansen Jan 2 '13 at 11:50
thanks, both of you :) – JustDanyul Jan 2 '13 at 11:54

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