how to externalize math formula in ruby?

[tester]

How to externalize a math formula in ruby?

I want to plot a series of y values per array of x's (alternatively, in range between two values, and at resolution of given points), according to a formula entered from outside.

[tester]

I'm getting an impression, that typical (?) programmers who use FS, too often say say "impossible".
Who to trust, when "no" is a "no"?
As a non-programmer, I don't understand the word "impossible".

I would understand a statement like "I don't know" or "let's figure out some logic behind and keywords to find out".

ruby-syntax compatible, can be entered via user's editbox.
div by 0 handling is specific to purpose I use it for.