# Sketching ln Graph: Tips & Advice for Solving Functions

• emma3001

#### emma3001

I have to sketch the following function:
y=x(lnx)^3

The ln scares me a bit... I have found the derivative of the function as 3(lnx)^2, and when making that equal to zero I got an anwer of around 0.7 if i remember correctly. This I guess is my critical number? Then the second derivative is 6/x(lnx). I really am not sure if I am doing this right, especially with the ln in there. Am I on the right track? What can I now do?

You'd better try the first derivative again. You'll need to use both the product rule and the chain rule.

You are missing one term:
it should be
[..]+6*log(x)/x

yep, so you are maximum points are wrong..
you should be getting
1.0000
0.0498

ignore what the thing is.. find values when function is max, and see if f^2 is positive for x>0 ...

I would use software like "Graph: padowan.dk
and my calculator (plugging in different values)

y=x(lnx)^3

6/x(lnx).

Hi emma3001! So try y=x(cos)^3, and y = 6/x(cosx). 