別解

(商の微分公式)

$$\begin{eqnarray*} y&=&\frac{\log x}{x}\\ y'&=& \frac{(\log x)'\times x-(\log... ...{\frac{1}{x}\times x-\log x}{x^2}\\ &=& \frac{1-\log x}{x^2} \end{eqnarray*}$$