How can I find the maximum curvature of $y = \ln x$?

Question

Title says it all. I know that you can use the following equation to find curvature (kappa) for a parametric curve, $$\frac{\|r'(t) \times r''(t)\|}{\|r'(t)\|} $$ but I don't know how to do this for regular functions. Answer is at the point $\left(\frac{1}{\sqrt2},\ln\big(\frac{1}{\sqrt2}\big)\right)$.

Answer 1

Oh I found the formula. Whoops. For anyone who's looking, it's: $$ \kappa = \frac{f''(x)}{(1+(f'(x))^2)^{2/3}} $$