Find the second order derivatives of the function.

Let $y=\log x$

Then,

$\frac{d y}{d x}=\frac{d}{d x}(\log x)=\frac{1}{x}$

$\therefore \frac{d^{2} y}{d x^{2}}=\frac{d}{d x}\left(\frac{1}{x}\right)=\frac{-1}{x^{2}}$