# Math Help - Second Derivative

1. ## Second Derivative

Find the second derivative:

$f(x)=x/(x^2+1)$

Thanks guys

2. Originally Posted by c_323_h
Find the second derivative:

$f(x)=x/(x^2+1)$

Thanks guys
I expect you are meant to use the quotient rule to do this, but since
I don't lnow it I will use the product rule:

df/dx= 1/(x^2+1) + x (-1)(2x)/(x^2+1)^2 = (x^2+1-2x^2)/(x^2+1)^2

.............= (1-x^2)/(x^2+1)^2

so:

d^2f/dx^2 = -2x/(x^2+1)^2 + (1-x^2) (-2) (2x)/(x^2+1)^3

..............= [-2x(x^2+1)=4x+4x^3]/(x^2+1)^3

..............= [2x(x^2=3)]/(x^2+1)^3

RonL

3. thanks. i liked the old MHF better. what happened to latex

4. Originally Posted by c_323_h
thanks. i liked the old MHF better. what happened to latex
Oh it's the same forum. LaTeX wasn't part of the last update and they are working on it. They're evidently having some sort of problem with it. It'll be back at some point and then the glory will return.

-Dan