can someone help me

[SMITH4]

Hi. I am not sure if I am posting in the right section. This problem is for my advanced alegbra/calc class. I have been in this board before so I just thought I would post here.

My problem reads

The percent of concentration of a certain drug in the bloodstream x hr after the drug is administered is given by K(x) = 4x / x ^2 + 9 . At what time is the concentration a maximum?

See I am confused because I don't know where to plug the numbers in the formula my book has. I don't even know if it is the write formula. My teacher just gave us this problem to work as a brain teaser for extra points. TRUST ME I NEED THE EXTRA CREDIT. SOme other class mates used a different formula and got 3 and 4 for the answer. I dont know if they are right, so if someone can give me some better infor I could use I would appreciate it, if not no big deal it is just for 5 extra credit points.


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Edit: Calculus question moved from "Intermediate Algebra" forum to "Calculus" forum. -- stapel

 

[pka]

\(\displaystyle \L
K(x) = \frac{{4x}}{{x^2 + 9}}\quad \Rightarrow \quad K'(x) = \frac{{4(x^2 + 9) - (4x)(2x)}}{{(x^2 + 9)^2 }}\).
Find where K’(x)=0.
Check for max or min.

 

[stapel]

See I am confused because I don't know where to plug the numbers in the formula my book has.

Which numbers? What formula?

Did the other tutor guess your meaning is the posted function?

Eliz.