Hello everyone

 

Pretty stupid: I was wondering how you can write "the derivative of a function f(x) in a" (to use in proofs), using [math]\frac{d}{dx}[/math], not just [math]f'(a)[/math]:

 

[math]\frac{df}{dx}_{x=a}[/math]?

 

[math]\frac{d}{dx}f(a)[/math]?

 

[math]\frac{df}{dx}(a)[/math]?

 

[math]\frac{df}{dx}_a[/math]?

 

Something else? Can someone help me on this one?

 

Thanks.

 

Function.

Edited December 2, 201312 yr by Function

At the point a

 

[math]\left. \frac{d}{dx}\right|_{a} f[/math] or [math]\left. \frac{df}{dx}\right|_{a}[/math] are common.

 

You want to be sure that no-one will think that your function is a function of a and not x.

At the point a

 

[math]\left. \frac{d}{dx}\right|_{a} f[/math] or [math]\left. \frac{df}{dx}\right|_{a}[/math] are common.

 

You want to be sure that no-one will think that your function is a function of a and not x.

Thanks.

 

P.S. What's the function of "\left." in your TeX code?

P.S. What's the function of "\left." in your TeX code?

It makes sure that the line on the right is tall enough.