Let M a $k$-dimensional manifold without boundary of $\mathbb{R}^{n}$ and N a $l$-dimensional manifold of $\mathbb{R}^{m}$ with or withour boundary. Show that $\partial(M\times N)=M\times\partial(N)$
My approach: First I prove that, if M a $k$-dimensional manifold of $\mathbb{R}^{n}$ and N a $l$-dimensional manifold of $\mathbb{R}^{m}$ then $M\times N$ is a manifold of $\mathbb{R}^{k+l}$ of dimension $k+l$. But now, I cannot see the relation $\partial(M\times N)=M\times\partial(N)$, any hint. Thanks!