Answer
$\frac{d^2y}{dx^2}=-2\sin x-x\cos x$
Work Step by Step
$y=xcosx$
$\frac{dy}{dx}=cosx+x\times{-sinx}$
$\frac{dy}{dx}=cosx-xsinx$
$\frac{d^2y}{dx^2}=-sinx-(sinx+x\times{cosx})$
$\frac{d^2y}{dx^2}=-sinx-(sinx+xcosx)$
$\frac{d^2y}{dx^2}=-sinx-sinx-xcosx$
$\frac{d^2y}{dx^2}=-2\sin x-x\cos x$