$x \cdot \cos x$

Let y $=$ xcos x
$\Rightarrow$ $\cfrac{{dy}}{{dx}} = x \cdot ( - \sin x) + \cos x = - x\sin x + \cos x$

$\Rightarrow$ $\cfrac{{{d^2}y}}{{d{x^2}}} = - [x\cos x + \sin x] - \sin x = - (x\cos x + 2\sin x)$