There is not always one solution.
https://gyazo.com/de488e0362aadcee07b450d1eb0ad8f0
Given quadratic function, most of the time there is either "no solution" or "two solutions". Quadratic functions "have only one solution" is as rare as linear functions "have no solution"
Similarly for general functions, "there is only one solution" is a rare case
In other words, linear function behavior is rarer in the whole function, but humans tend to misinterpret things as if they were linear functions
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