# Talk:Derivative

What a surprise--once again, a page in desperate need of revision. I'll do my best to delete absurd and meaningless statements, but someone else needs to come here and do a complete rewrite.--Mathoreilly 13:42, 2 July 2008 (EDT)

So the page is at least a little less wrong now, but someone still needs to do something about the max/min section which is, to put it bluntly, very poorly written.--Mathoreilly 13:53, 2 July 2008 (EDT)

Someone other than you, apparently. Sorry, but I think a red link would be better than what you left us with.
I have taught SAT math and I earned AP credit for calculus. This was simply unacceptable quality. Do not edit any more math articles. --Ed Poor Talk 14:41, 2 July 2008 (EDT)

I have taken this out as suggested by Mathoeilly as it needs work, possiblly a different article,

Thus the derivative is a measurement of how a function changes when the values of its inputs vary. Derivatives are helpful in determining the maxima and minima of a function. For example, taking the derivative of a quadratic function will yield a linear function. The points at which this function equals zero are called critical points. Maxima and minima can occur at critical points, and can be verified to be a maximum or minimum by the second derivative test. The second derivative is used to determine the concavity, or curved shape of the graph. Where the concavity is positive, the graph curves upwards, and could contain a relative minimum. Where the concavity is negative, the graph curves downwards, and could contain a relative maximum. Where the concavity equals zero is said to be a point of inflection, meaning that it is a point where the concavity could be changing. Also, differentials have numerous applications in physics.

## The current article

Okay I will make a list of questions about the article

1. In what contacts do you mean "measure"? Measure has a very specific mathematical meaning how do you mean it.
2. You link to tangent but if you look at the tangent article it discusses the tangent function and even then not in a way you can under stand the tangent function.
3. "differentiation is the reverse process of integration" In all my years of doing maths I have never heard anyone use the word process unless they are discussing and actual physical process. I think the term you are looking for is operation.
4. You then go on to talk about maxima and minima. This is all good but as we at now stage have found out anything about how to differentiate it is usless to the reader.

The notion "Differentiability implies continuity as well as integrability" is at least misleading. You want to say - I suppose - that, if a function is differentiable (and therefore continuous) in a point (and therefore in a neighborhood of this point), then there exists a primitive for this function on this neighborhood. Integrability of a function f(x) on $\mathbb{R}$ OTOH is commonly understood to be the existence of $\int_{\mathbb{R}}f(x) dx$ - and the simple example of f(x) = sin(x) shows that the Integral of this differentiable function does not exist.--DiEb 17:01, 17 August 2008 (EDT)