Let $\varphi$ be the map from $\mathrm{O}(n) \times \mathcal{S}_n^{++}(\mathbb{R})$ to $\mathrm{GL}_n(\mathbb{R})$ defined by $\varphi(O, S) = OS$ for every pair $(O, S)$ of $\mathrm{O}(n) \times \mathcal{S}_n^{++}(\mathbb{R})$.
Show that $\varphi$ is bijective, continuous, and that its inverse is continuous.