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In mathematics, f and g are common names for arbitrary functions. The first appearance of these named prefixes was on the HP-65, which had f, f^(-1), and g, as you can see in this very museum. I think HP took these letters from math - but that's just my personal view.

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Quote:

I am wondering about the motivation of HP developers to label the prefix keys of the RPN calculators in the 70s and 80s by the letters **f** and **g**. Obviously, the reason was not absolutely substantive as later angled arrows were invented instead.

I don't know the official reason, but I always assumed that since f and g were common names for functions (f(x), g(x)), HP used f and g as names for alternate functions.

Eddie

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Now a better question - when did the practice of using f(x) and g(x) for functions originate? The earliest calculus textbook I have from late 1800s already used f(x) and g(x). Does this originate back to Sir Isaac Newton himself?