Derivative and horizontal tangent help

[kings13]

Derivative and horizontal tangent help!

Homework Statement

Determine the point at which the graph of the function has a horizontal tangent line.

Homework Equations

http://www.webassign.net/cgi-bin/symimage.cgi?expr=f(x) = (8 x**2)/(x**2+8)and f(x)=x/ root2x-1endroot

The Attempt at a Solution

128x/(x^2+8)^2? no idea what I am looking for really

 

[JThompson]

Your link was faulty. I have no idea which function you're referring to, but generally a horizontal tangent line is found where y'=0.

 

[The legend]

yup there's a 404 not found error.

 

[kings13]

fixed the link but I am having trouble finding the derivative.

 

[MysticDude]

just use the quotient rule. the derivative of g(x)/f(x) = \frac{f(x)g'(x) - g(x)f'(x)}{f(x)^2}.EDIT: I highly recommend using Wolfram Alpha if you really get stuck. It has a show steps buttons on most derivative question!

 

[kings13]

http://www4a.wolframalpha.com/Calculate/MSP/MSP93419cd13d43b6e511700000d6f885345b6b5d7?MSPStoreType=image/gif&s=44&w=296&h=42


it says that is the answer. but that's not my problem, what is the coordinates to the answer? I am not sure what I am looking for

 

[MysticDude]

http://www4a.wolframalpha.com/Calculate/MSP/MSP93419cd13d43b6e511700000d6f885345b6b5d7?MSPStoreType=image/gif&s=44&w=296&h=42 it says that is the answer. but that's not my problem, what is the coordinates to the answer? I am not sure what I am looking for

Well, you can't really plug anything into the derivative to make it zero. So I'm thinking that there won't be horizontal tangent in that equation.