別解

$${y=\frac{x}{\sqrt{x-1}}}$$

$$\begin{eqnarray*} y&=& x(x-1)^{-\frac{1}{2}}\\ y'&=& x'(x-1)^{-\frac{1}{2}}+... ...(x-1)^{-\frac{3}{2}}\\ &=&\frac{1}{2}(x-2)(x-1)^{-\frac{3}{2}} \end{eqnarray*}$$