Recent content by Phoeniyx

The slope is = {f(x + h) - f(x)} / h, where h tends to 0, from a general sense. Since SammyS was nice enough to type out the derivative for f(x) = x^{3}, the answer at x = 0 is h^{2}, , where h can be arbitrarily made close to 0. The LIMIT when evaluated is obviously 0.. No arguments here...

All I am asking you guys to do is to respectfully consider what the word "limit" means.. As in please look under the hood. SammyS, your derivation above is obviously correct, and what I am trying to say in this thread is staring right back at you. f(x + h) and f(x) on the first line are two...

I understand perfectly well what is meant by a "limit" concept, as I described above. Now, just to re-iterate what YOU said: (your words below, not mine - copy/pasted) "a slope does not require two points to calculate it" (few posts above) "derivative (= slope)" (from above post) Combining...

Lets keep the discussion academic shall we? I don't plan on doing any "damage" with my calculus. In any case, if you go to the basic definition of a derivative {f(x + h) - f(x)} / h, where h -> 0, that IS taking two points on the curve. I am not "making it up" as you say. Just need to go to the...

I get what you guys are saying. Ok, here's my process of convincing myself... As some of you have said h(x)=x^{3} has similar properties as f(x) (from the original post). I would have had the same reservations that I indicated for f(x) with h(x), except that the same would be present with...

But, it's 0+ on one side and 0- on the other, and obviously "0" at 0. From a purist perspective (whatever that means), the tangent will never be "horizontal" - even though it can be made infinitesimally close to it. But, the question is not asking for the latter, but the former ("horizontal")...

Hey guys. This question is really bugging me. (Please see question #63 here: http://www.ets.org/s/gre/pdf/practice_book_math.pdf) - written below for your convenience. f(x) = xe^{-x^{2}-x^{-2}}, x \neq 0 f(x) = 0, x = 0 (apologies for not knowing the itex command do write this as a single...

Hi DrDu. I am sorry, but I am not understanding your response. Could you please elaborate a bit further? Thank you.

Thanks that helps!

Hey guys. I am going through the PRM (risk manager) material and there is a sample question that is bugging me. The PRM forum is relatively dead, and they don't usually go that deep into the theory anyway. So wanted to ask you guys. Shouldn't a random vector always have a covariance matrix? Why...

Hey guys. I have some trouble understanding how the F-test is used for testing the viability of a regression model. Before I delve into the background/question, just wanted to post a link that discusses the topic briefly: http://www.stat.yale.edu/Courses/1997-98/101/anovareg.htm So, coming...

Thanks R136a1. That was very helpful. Appreciate you taking the time for a detailed explanation.

Excellent. Thank you. Wasn't sure what to search for.

Thanks Gridvvk. What you said in the [Edit] section does provide some solace :). I guess "proof of second derivative test" is what I should Google for? It's interesting what you said that f_{xy} = f_{yx} for "most" conditions. Always presumed it to be the case for "all" conditions. Can you...

Thanks. But what I meant was what happens when f_{xx} and f_{yy} have the same sign - but their product is less than [f_{xy}]^2. So, your example would not work since 2 and -2 have opposite signs. Essentially, what I am asking is, what does it mean for a curve to have f_{xx} = 2, f_{yy} = 1...