I have the function [tex] \[y = \sqrt x - 4\ln (x)\][/tex](adsbygoogle = window.adsbygoogle || []).push({});

I find the derivative to be [tex] \[y' = \frac{{\sqrt x - 8}}{{2x}}\] [/tex]

When finding the critical numbers of y' I look for where the derivative

is equal to zero or where the derivative is undefined. So where y' is

equal to zero is when x=64. y' is undefined when x=0, but when x=0

the original function is also undefined. Since x=0 makes the original

function undefined can I exclude it from my critical points? I am thinking

I am able to since x=0 isn't even in the domain of y.

Thanks

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Critical numbers of this derivative

**Physics Forums | Science Articles, Homework Help, Discussion**