Question

Hi! I have a question concerning derivatives :)

Answer 1

\[\frac{ d }{ dx }(4-x^{2}-\frac{ 16 }{ x^{2} })\]

Answer 2

Now, according to Wolfram|Alpha, the correct answer is\[x=\pm2\] I just don't know how to get there :P

Answer 3

Here's what I did:\[\frac{ df }{ dx }=-2x-16(\frac{ -2x }{ x^{4} })\]\[=-2x+\frac{ 32x }{ x^{4} }=-2x+\frac{ 32 }{ x^{3} }\]

Answer 4

btw, df/dx=0

Answer 5

Then I factor out the x, right?\[=x(-2+\frac{ 32 }{ x^{4} })=0\]

Answer 6

I kinda know how to get to x=+/-2, I just don't know why I don't get x=0 as well :/

Answer 7

Look at the graph; there is a horizontal asymptote at x = 0.

Answer 8

It is not in the domain. I mean x =/= 0

Answer 9

Ooooh, of course! :P Thanks a lot! :P

Answer 10

http://en.wikipedia.org/wiki/Division_by_zero