### How to get a field extension by adjoining elements

Let $\alpha_1,\alpha_2,\ldots,\alpha_n \in \mathbb{R}$. How to define the field extension $\mathbb{Q}(\alpha_1,\alpha_2,\ldots,\alpha_n)$ in sagemath and how to compute the degree of the extension $[\mathbb{Q}(\alpha_1,\alpha_2,\ldots,\alpha_n):\mathbb{Q}]?$