# Smart Ass Question on the Deriviative of f(x) = |x| **URL:** \ **Category:** Factual Questions\ **Created:** [August 17, 2005, 11:42pm UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502 "2005-08-17T23:42:15Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![mojave66](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@mojave66](https://boards.straightdope.com/u/mojave66)\ **Post date:** [August 18, 2005, 8:24pm UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502/21 "2005-08-18T20:24:33Z")
> [@Thudlow Boink](#): > > A similar argument shows why a[sup]0[/sup] = 1, not 0, when a is a nonzero number. Thanks for this. Mojave (feeling very stupid these days) ---
**Author:** ![mojave66](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@mojave66](https://boards.straightdope.com/u/mojave66)\ **Post date:** [August 18, 2005, 8:33pm UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502/22 "2005-08-18T20:33:14Z")
> [@Mathochist](#): > > You can’t just “set” values for the derivative. It’s a specific function, completely determined by f and defined only where f is differentiable. You can construct a function g(x) like you want, but the best you can then say is that g(x) = f’(x) where both are defined. Well, I wasn’t setting values for the derivative, but rather for the function itself. Granted, my mistake was thinking of 0 as a constant rather than a point. And, since |x| is continuous function, I jumped to a bad conclusion about the derivative of 0 (which, ftr, I did know that it didn’t exist even by my definition of |x|. I did say it was a “smart-ass question” in my title.) Mathochist, gimme a break here. I’m incredibly rusty, I’ve spent the last year without any mathematics at all just trying to keep shit together. Of course reading about the gamma function made me go “D’oh!” but only in the context of “I was somewhat acquainted with it at some point in the past, yes.” ---
**Author:** ![tim314](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tim314/32/3468_2.png) [@tim314](https://boards.straightdope.com/u/tim314)\ **Post date:** [August 18, 2005, 10:04pm UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502/23 "2005-08-18T22:04:46Z")
> [@mojave66](#): > > Oh, and FTR I’m technically female, but will answer to either gender. My bad, I was just playing the odds with “he” (since I’m guessing the majority of statistics majors are male). > [@mojave66](#): > > Mathochist, gimme a break here. I’m incredibly rusty, I’ve spent the last year without any mathematics at all just trying to keep shit together. I’m sure your misstatements about derivatives are just rust as you say (sorry if I implied otherwise), but that said, I don’t think **Mathochist** or anyone else has been particularly harsh in correcting them. ---
**Author:** ![mojave66](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@mojave66](https://boards.straightdope.com/u/mojave66)\ **Post date:** [August 18, 2005, 11:09pm UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502/24 "2005-08-18T23:09:10Z")
> [@tim314](#): > > I’m sure your misstatements about derivatives are just rust as you say (sorry if I implied otherwise), but that said, I don’t think **Mathochist** or anyone else has been particularly harsh in correcting them. Nah, I’m just feeling intellectually deficient & defensive, my apologies for being so. I mean, I read the answers here and I think “soooo… why didn’t _I_ think of that?” \ ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [August 19, 2005, 2:19am UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502/25 "2005-08-19T02:19:13Z")
> [@mojave66](#): > > Well, I wasn’t setting values for the derivative, but rather for the function itself. You _just_ colloquially restated your question as “hey, what if we set f’(0)=0?”. No matter which f you meant that to apply to, it’s still nonsensical on its face. > [@](#): > > Mathochist, gimme a break here. And get sloppy, soft statisticians? Now drop and give me 20! ---
**Author:** ![mojave66](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@mojave66](https://boards.straightdope.com/u/mojave66)\ **Post date:** [August 19, 2005, 5:07am UTC](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502/26 "2005-08-19T05:07:14Z")
> [@Mathochist](#): > > And get sloppy, soft statisticians? Now drop and give me 20! Yes sir! 1, 2, 3, er… what’s next? 😃 [Previous page](https://boards.straightdope.com/t/smart-ass-question-on-the-deriviative-of-f-x-x/317502.md?page=1)