How to Determine Where a Function is Concave Up or Down?

[hahaha158]

Homework Statement

f(x)=(2x)/((x^2)-25)

find concave up and down

Homework Equations

The Attempt at a Solution

I found the second derivative to b

-4x((-2x^2)-24)
-----------------
((x^2)-25)^2

i found the only inflection point was x=0 (which was correct)

I plugged in values on both the right and left side of 0 and determined that f(x) was concave down on all values smaller than 0 with the exception of -5, and f(x) was concave up on all values larger than 0 with the exception of 5

however this is not the correct answer. Can someone confirm/tell me what i am doing wrong?

thanks

 

[LCKurtz]

Something is wrong with your calculations as that is not correct for the second derivative.